random. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. In each case we will compare the execution speed of a code segment before and after applying the technique. This fills the ith row of newArray with the current values in array. Description. In MATLAB®, you can create timetables and assign data to them in several ways. When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. For very large arrays, incrementally increasing the number of cells or the number of elements in a cell results in Out of. preallocate array without initializing. For the first function shown above In order to work around this issue, you should pre-allocate memory by creating an initial matrix of zeros with the final size of the matrix being populated in the FOR loop. Create a timetable from a vector of row times and data arrays by using the timetable function. If you pre-allocate an object array, the effects will be tiny, when the overhead for creating the vector of object pointers is negligible compared to the costs of the object constructor. When you assign them to the cell element, the former contents is overwritten. X (10000,10000) = 0; This works, but leaves me with a large array of zeroes. Preallocating a large array in a MATLAB matfile with something other than zeroes. 1. Incremental growth of an array by concatenation (use of horzcat, vertcat, cat, or []) forces MATLAB to dynamically reallocate memory each time the array grows in size. MATLAB® fills the first to penultimate array elements with default ObjectArray objects. The problem is that: each array field can be 2 or 3 chars, like: 'C4' and 'C#4'. F (fr) = getframe ( hFig_cp ); end. The reason why you have the cells in the second column is because you are assigning both pairs to the first column by using couples{k},if you want to assign the names from name2 to the first columns of the cell array use couples{k,1}, and for name1 to the second column of the cell array use. Rough guidelines: One that is pre-allocated is better. Recently, I had to write a graph traversal script in Matlab that required a dynamic stack. For example, if C does not already exist, these statements are equivalent: MATLAB creates. You can also create an array of SimpleValue objects by constructing the last element of the array. . Can anyone help me to fix pre-allocation memory for a structure output? I have a structure function which have 18 elements, it has two imputs and give results 16 outputs and two inputs. What is the correct way to preallocate an object array? Theme Copy classdef MyobjectArray properties value = []; % an array of MyData objects end methods. C = 0x0 empty cell array. So, this is the same as for matrices, where e. Because you do the loop backwards all variables start at maximum size and space is allocated at once. It takes a long time to allocate, but finishes. Choose a web site to get translated content where available and see local events and offers. I haven't done extensive testing. In order to work around this issue, you should pre-allocate memory by creating an initial matrix of zeros with the final size of the matrix being populated in the FOR loop. As there are lots of frames to be obtained, I am trying to pre-allocate the array for the frames using repmat (): Theme. T = table ('Size',sz,'VariableTypes',varTypes) creates a table and preallocates space for the variables that have data types you specify. 268]; (2) If you know the maximum possible number of columns your solutions will have, you can preallocate your array, and write in the results like so (if you don't preallocate, you'll get zero-padding. . Name Size Bytes Class Attributes y 1x1 1 uint8. In MATLAB®, you can create tables and assign data to them in several ways. A = [77 65 84 76 65 66]; C = char (A) C = 'MATLAB'. Preallocating a Nondouble Matrix When you preallocate a block of memory to hold a matrix of some type other than double , avoid using the method. Preallocate a timetable and fill in its data later. preallocate array without initializing. cell also converts certain types of Java ®, . (here a=1:1000; would be even better) For objects the pre-allocation works by assigning one of the objects to the. When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. If I had a 1000 tables, it would be nice if Matlab could index them: T (1) = T1; T (2) = T2; for i = 1:1000. for i=n:-1:1. Find more on Operators and. cell array of empty matrices. MATLAB tries to offer a lot of guidance on when and how to preallocate. MATLAB clearly describes and recommends this in their documentation:mystructure. Sign in to answer this question. The insight here is that. So any cell array and vector can be predeclared with, e. How to pre-allocate a 3 dimensional array in matlab. Concatenate the arrays, and then simply index against the parts you need. str = strings (sz1,. Learn more about preallocation, matrix, vercat, speed, pre-allocation, empty matrix MATLAB. Using repmat is by far the most efficient way to preallocate structs : N = 10000; b = repmat (struct ('x',1), N, 1 ); This is ~10x faster using Matlab 2011a than. MATLAB is an abbreviation for "matrix laboratory. There are two ways to fix the problem. Learn more about array preallocation, performance . The standard example is as follows. It looks like this method is a little faster for small arrays (~100 datetime objects), but repmat() is quite a bit faster for large arrays (~1 million datetime objects). For example, if you create a large matrix by typing a = zeros(1000), MATLAB will reserve enough contiguous space in memory for the matrix 'a' with size 1000x1000. ,sn defines the dimensions of the array. g. Each page of the rotation matrix array corresponds to one element of the quaternion array. I saw, here on the forums, a way to deal with dynamic arrays by preallocating a "big enough" array before the loop and trimming the unnecessary data afterwards. For the most part they are just lists with an array wrapper. You should use getfield function to access the timestamp char array from the data struct altogether in a single line without using loops. If you grow one with for instance push or pop the JS engine needs to do a lot of additinal steps. Learn more about array preallocation, performance . A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. You know how many passes through the loop. If you must use a for-loop, you should pre-allocate the array. Learn more about create tables with large numbers of variables MATLAB I want to create tables with a large number of variables (i. For example, strings(3,1,1,1) produces a 3-by-1 vector of strings with no characters. Simply create the array once and measure its length. Preallocation makes it unnecessary for MATLAB to. Learn more about random number generator. X (10000,10000) = 0; This works, but leaves me with a large array of zeroes. But now it can run in forward direction also. . Learn more about matrix array, out of memory . Find the treasures in MATLAB Central and discover how the community can help you! Start Hunting!In MATLAB®, you can create timetables and assign data to them in several ways. For very large arrays, incrementally increasing the number of cells or the number of elements in a cell results in Out of. clc; clear all; I = zeros(151,151); W=64; %locs=zeros(151,1); for x = ; y = ; end. b(m)?. a (2,2) = SimpleValue. Theme. Then stuff one cell at each iteration of the loop. Pre-Allocate Space for a Cell Array. g. 2. Finally, inside the fuller explanation is a link to the section of the MATLAB documentation already mentioned in this post. empty((10,),dtype=object)Preallocate Arrays of Graphics Objects. Learn more about array preallocation, performance . Find more on MATLAB Report Generator in Help Center and File Exchange. This does two things, It fixes the truncation problem, and it also avoids the unnecessary expansion step using repmat(). Life would be easy to pre-allocate if dimensions are known, if not you have to follow some other procedures. grade_list = zeros(1,100); % approximately 100 students in class names = cell(1,100); % approximately 100 names for the students in classPreallocate the array before the body of the loop and simply use slicing to set the values of the array during the loop. cell also converts certain types of Java ®, . In fact there is an unofficial mex routine mxFastZeros that seems to tap into this. array of structs how to preallocate and assign. tab(r, c) = something %indexing. this code have only 1 point for each 405 data. create 3D (n:m:k) matrix in matlab using array 2D (i:3) 1. s = struct (field,value) creates a structure array with the specified field and value. mean "associated with the index". objarray = gobjects(1,5); objarray(1) = f; objarray(2) = ax; objarray(3) = p; objarray(4) = txt1; objarray(5) = txt2; objarray. F (fr) = getframe ( hFig_cp ); end. mat file on disc. . I would preallocate the array, then do the array2table call at the end,. Puting empty value in numeric array. I always am hesitant to pre-allocate as zero array since zeros from pre-allocation can be mistakenly read as data if you made a mistake in your code. Preallocating Cell Arrays with the cell Function. Solution 1: In fact it is possible to have dynamic structures in Matlab environment too. In Matlab, arrays are dynamic in size, meaning, whenever you need a larger array, you can just index. MATLAB provides these functions to create event tables from input data, filter timetable rows on. You can then add graphics objects to the array. (For primitive types. If you pre-allocate an object array, the effects will be tiny, when the overhead for creating the vector of object pointers is negligible compared to the costs of the object constructor. 075524 Preallocate Using indexing: 0. This is because when a cell array is resized only the pointers/headers for the cell data needs to be moved from the old location to the new one. The array a is a 3-by-3 array; we can add a third dimension to a, by providing the values like −. Option 3. Theme. Matlab tells me to preallocate my array, but I cant figure out how to do that. Copy. Pre-allocate simple things (like numeric matrices or the top level of a cell array structure). u is from 1 to n. Put a semicolon at the end of your x (k) = x (k-1)+5 line and it'll process it near instantly: Theme. Is there a way to create and preallocate for. To preallocate, before you start the loop, just write. And doing it in minimum time is also. One of the first things one learns about programming efficiently in MATLAB is to avoid dynamically resizing arrays. str2double is suitable when the input argument. . Then, change the contents but not the size of symbol_chip. I want to save each OVR_MEAN in a different column since each column represents an emission constituent for me and that is why I am indexing it. Learn more about struct, structures, memory MATLABHow to preallocate 3 D matrix?. Each time you go around, your elseif block is resizing symbol_chip, which is expensive. Pre-allocating cell arrays. rand(1,10) Here, we allocate the memory only once. sz is a two-element numeric array, where sz (1) specifies the number of rows and sz (2) specifies the number of variables. How to make a preallocated array in matlab. Convert a numeric array to a character array. Create Ordinal Categorical Array by Binning Numeric Data. When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. I want to make a character array consisting of 3 rows and 2 strings and firstly I dont know how I can preallocate it. This is because. The last one is useful if you construct a linear array but then. So, i will have n different output(:,:) matrix's which i am saving in outp(:,:,u). To specify the row times, you can either use an input vector of row times or create the row times by using a sample rate or time step. In other words, if: two arrays share the same dimensions except for one; and. 531e+10 bytes) *. Copy. MyNewField = serial ('COM3'); %completely different type is OK! When you make an assignment to all of an ordinary MATLAB variable, or you make an assignment to all of a particular structure array field name, then the memory used for the expression on the right hand side is. As there are lots of frames to be obtained, I am trying to pre-allocate the array for the frames using repmat (): Theme. The third method is slower than the second because it preallocates the matrix but with no specific size, the. How do I pre allocate an array in MATLAB? Following is an example on how to pre-allocate memory before entering a FOR loop: x=zeros (30); for i=1:30, for j=1:30. Using this new object, you can very easily create an array of strings in a loop as follows: for i = 1:10 Names (i) = string ('Sample Text'); end. In order to work around this issue, you should pre-allocate memory by creating an initial matrix of zeros with the final size of the matrix being populated in the FOR loop. Preallocate a table and fill in its data later. What does Preallocating mean in MATLAB? Preallocating a Nondouble Matrix. This works. STRVCAT automatically pads the ends of the strings with spaces if necessary to correctly fill the rows of the matrix: >> string1 = 'hi'; >> string2 = 'there'; >> S = strvcat (string1,string2) S = hi there. % Prealloca. I understand that one can easily pre-allocate an array of cells, but this isn't what I'm looking for. right click and to tell MATLAB to not show that warning. For more information, see Access Data in Cell Array. Yes. Show -1 older comments. An empty array in MATLAB is an array with at least one dimension length equal to zero. . x is the input of an experiment and y is the measured value. ones, np. head = struct ('number', cell (1, 10), 'pck_rv', cell (1, 10)); Now head is a [1 x 10] struct array withe the fields 'number' and 'pck_rv'. When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method. ; creating a large vector twice: first length(0:increment:end_time), then later mTime = 0:increment:end_time;. This can be accomplished with the matfile command, which allows random access to a . If the size of any dimension is 0, then str is an empty array. It appears (to me anyway) that MATLAB keeps a store of 0-filled memory in the background for use in cases such as this. That's a lot of excess overhead when one knows a priori the size of the resulting array. When using categorical arrays, you can easily: Select elements from particular categories. field1=a; my_struct_data. 3 ältere Kommentare anzeigen. Preallocation makes it unnecessary for MATLAB to resize an array each time you enlarge it. Initialize and allocate memory for a cell array. Preallocating the array with either zeros or NaN's takes matlab several seconds to initialize the array. empty(0,5) still preallocate 5 "slots" of memory ?" - To be formal: No. This question has appeared before, but there are two options I didn't see in that thread. Questions: Would there still be a benefit in truly pre-allocating the array memory - or would MATLAB, just as it does inside the loop, even during pre-allocation just try to allocate single memory blocks for each array element alone?. Date as Array Element in MATLAB. Example:Convert Integers to Characters. np. That one however could be created after the loop. %I kept number of columns to be constant (5) because you used X= [X;A] %in the question which means. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. , An along dimension dim. But now it can run in forward direction also. The first thing to note is that MATLAB has improved automatic array growth performance a lot in recent versions, so the performance hit implied by the warning might not be too bad if you do it right (see below). So, here I first allocate memory for 8 cells in the cell array and then I wish to reach each of these 8 cells by writing data {1:8} and add a NaN-matrix in each of them. Writing v(2000)=0 causes matlab to allocate the missing space in one step. C=cell (1,N) it is like you are creating N separate MATLAB variables except that they do not have distinct names (x,y,z, etc. Creating the array as int8 values saves time and memory. and. If you want to make a double 2-by-2 array, use zeros, ones, rand, eye, etc. Use the gobjects command to preallocate an array of graphics objects. But, in Matlab, look to vectorize and eliminate loops entirely -- in your case just write. But when you change the values, an addition deep copy is performed for each element, which consumes more time than allocating the different arrays of the fields in a loop. {0×0 double} {0×0 double} Matlab need more room, so it allocates a new array of size dim1 x dim2 x 2, copy over the content of the previous array in (:, :, 1) and fill (:, :, 2) with the new result. For example, let's create a two-dimensional array a. Below is the class that I am using in MyobjectArray class classdef MyData properties x = []; % a column vector of data e. To create a missing string, convert a missing value using the string function. 3]; a {2} = [1, 0, . for i = 1 : 10. Preallocating Memory. Hi All, I am trying to read 150 text files. For very large arrays, incrementally increasing the number of cells or the number of elements in a cell results in Out of. I want to manipulate the images. A = int8 (zeros (100)); This statement preallocates a 100-by-100 matrix of int8, first by creating a full matrix of double values, and then by converting each element to int8. So the problem is if I want to do any calculation with the rows, I will end up including rows 2,3,4 which are now 0, this messes up with my calculations. Compare these two similar operations:Divide that by the number of bytes per element of your array (8 for doubles) and you know the max number of elements you can preallocate. The only variable whose size is unknown at the beginning of the loop appears to be TotLabel. Now the final size of the struct array is created in the first iteration. That is, graphics arrays can be heterogeneous. 4. My doubt is how to apply this method for this specific case, since here, at each iteration i don't know by how much the "resultPolygon" data grows, and, in general, any. MATLAB works with fixed-size memory chunks. It appears (to me anyway) that MATLAB keeps a store of 0-filled. There is absolutely no point in making D a cell array since each cell is only going to contain a scalar. z=zeros (2); % is a 2x2 array. When you create an object array this way, MATLAB ® takes one of two approaches to fill in the rest of the. Learn more about cell arrays . Related. If I skip pre-allocation, the output will give me 1*1000 structure. Preallocation is actually very easily done in matlab, in your case just by changing one line of code. F = false (sz) is an array of logical zeros where the size vector, sz , defines size (F). According to our records, this is the primary and most recent file release from MathWorks. For example, if you create a large matrix by typing a = zeros (1000), MATLAB will reserve enough contiguous space in memory for the matrix 'a' with size 1000x1000. It need no longer reallocated at each iteration, because it will no longer need to change size at every step. 0 x 5 = 0 elements, so it allocates 0 bytes of raw data. e. For example, if you create a large matrix by typing a = zeros (1000), MATLAB will reserve enough contiguous space in memory for the matrix 'a' with size 1000x1000. You can use a buffer. Here's a general approach to preallocate memory for an array in MATLAB: Identify the variable that changes size during each loop iteration. I would like to preallocate a char array, fill it with data and then add this array to a table column. As such, should this cell array be non-empty, we have found at least one common word between C and D. After you preallocate the array, you can initialize its categories by specifying category names and adding the categories to the array. g. This does not work but gives me: Apparently the 1:8 syntax does not work inside. . Use the appropriate preallocation function for the kind of array you want to initialize: zeros for numeric arrays strings for string arrays cell for cell arrays table for table arrays Preallocating a Nondouble Matrix When you preallocate a block of memory to hold a matrix of some type other than double, avoid using the method Pre-allocating an array is always a good idea in Matlab. Answers (1) To preallocate the object array, assign the last element of the array first. cell also converts certain types of Java ®, . preallocate array without initializing. P , such that writing values later on will consume additional time by creating deep data copies at first. Create a string array where every element is an empty string. . This is the difference between Virtual Memory and Physical Memory. Actualy the simplest and fastest solution to this problem is to not attempt to create an empty struct. The best solution, whenever possible, is to pre-allocate. C = horzcat (A,B) concatenates B horizontally to the end of A when A and B have compatible sizes (the lengths of the dimensions match except in the second dimension). And to answer your question "does preallocating memory makes a simulation run faster?", then answer is yes!In most cases array preallocation will give much faster code than without array preallocation. a=sym (zeros (50000,1)); Filling the area with relatively simple expression e. This can result. There is a way to preallocate memory for a structure in MATLAB 7. #Syntax. I always am hesitant to pre-allocate as zero array since zeros from pre-allocation can be mistakenly read as data if you made a mistake in your code. a=zeros (5,5) for j=1:4:5. expanding arrays inside loop without array preallocation: for large arrays this is very inefficient as the array must get moved in memory each time it changes size. varTypes specifies the data types of the variables. The number of cells of the cell array is fixed at NrInt. If you look at the notation MATLAB uses to append to a matrix, it almost explains itself: >> a = zeros (1, 3) a = 0 0 0 >> a = [a 1] a = 0 0 0 1. The reshape function changes the size and shape of an array. Here, an example of preallocation and filling with loop. Each element is a string with no characters. I want to preallocate a structure that contains many fields. Pre-allocate in general, because it saves time for large arrays. Preallocate a cell array instead. In our case, C and D would be a cell array of words separated by spaces from A and B. At the end, just collapse the cell array into a flat array using cell2mat. While this may make sense due to the high number of controls - spread over three arrays - the deletion of the controls is also pretty slow, altough the code is pretty simple: Theme. Right now I am using an empty cell array cellarrayA = cell(N,1), and putting each object into the cell, like cellarrayA(n) = ClassA(input(n)). . A (end+1) = elem; which works for both row and column vectors. for jj= nFrames:-1:init_frame. a = zeros (1,100); x = complex (a,0); To verify that the above command actually creates a 100-by-1. There are a number of "preferred" ways to preallocate numpy arrays depending on what you want to create. a = 2×2 SimpleValue array with properties: prop1. Creating the array as int8 values saves time and memory. Empty arrays are useful for representing the concept of "nothing. Use the semicolon operator to add new rows. I want to save each OVR_MEAN in a different column since each column represents an emission constituent for me and that is why I am indexing it. But even then implement a proper pre-allocation simply to care about good programming practice. So, here I first allocate memory for 8 cells in the cell array and then I wish to reach each of these 8 cells by writing data {1:8} and add a NaN-matrix in each of them. You pre-allocate only the cell: Theme. Initialize a cell array by calling the cell function, or by assigning to the last element. The short answer is A = nan (5, 10) in MATLAB is equivalent in semantic to A = fill (NaN, 5, 10) in Julia. N = 1000; % Method 0: Bad clear a for i=1:N a (i). The first time, MATLAB assigns a value to c (5). Then, useful functions are. Theme. Consider these programming practices to improve the performance of your code. Use the gobjects function to preallocate arrays for graphics objects. Preallocating Cell Arrays with the cell Function The cell function allows you to preallocate empty cell arrays of the specified size. H = gobjects (s1,. a (2,2) = SimpleValue. P] = deal(P) creates shared data copies for the contents of all S(:). I haven't done extensive testing. The problem lies in the fourth line. If you know what is stored in each column, create the variables and add the rows as you go. Use a structure array. If you place matrices in each cell location C {i}, then the matrix content of each C {i} individually will occupy contiguous. I am trying to preallocate the array in this file, and the approach recommended by a MathWorks blog is. ) Matlab allocates memory for the total number of elements in the array, which is equal to the product of all dimensions. Create a timetable from input arrays or preallocate space for variables whose values are filled in later. This fills the ith row of newArray with the current values in array. Hmm good point. 0. % Prealloca. Recently, I had to write a graph traversal script in Matlab that required a dynamic stack. Copy. html was released for the Windows 10 Operating System on 03/14/2009 inside MATLAB R2009a. 0. To preallocate, before you start the loop, just write. Copy. Create a timetable from a vector of row times and data arrays by using the timetable function. 063774 Preallocate with repmat: 0. Is there a better way of preallocating a cell array of empty chars than using a for loop or deal? Cells can contain any data type, yet if I create a empty cell array, it is always type double. Preallocate a 4-by-1 array: h = gobjects (4,1); Assign axes handles to the array elements: tiledlayout (2,2) for k=1:4 h (k) = nexttile; end. The alternative is to have an array which grows during each iteration through a loop. Theme. I mean, suppose the matrix you want is M, then create M= []; and a vector X=zeros (xsize,2), where xsize is a relatively small value compared with m (the number of rows of M). However, each cell requires contiguous memory, as does the cell array header that MATLAB ® creates to describe the array. Then, fill X and when it is filled, just concatenate the matrix with M by doing M= [M; X]; and start filling X again from the first. It appears (to me anyway) that MATLAB keeps a store of 0-filled memory in the background for use in cases such as this. I also tried to store values in it ( in the first row) using. MATLAB Language Fundamentals Operators and Elementary Operations. For example, you can concatenate the handles of the figure, axes, and. To specify the row times, you can either use an input vector of row times or create the row times by using a sample rate or time step. Toc = sym (zeros (1,50)); A double array is allocated and then recast as symbolic. The second time, it assigns the result of a second call to randi to create c (1). zeros((10000,10)) for i in range(10000): arr[i] = np. ,sn) returns an s1 -by-. Learn more about pre-allocate memory for a structre output, preallocation, structure, struct MATLAB. Also consider to use array of objects, instead of cell array of objects. Data = [Data,var1]; end. Copy. But in order to use the empty method, the size of the array you want to create must be 0 in at least one of its dimensions. zeros, np. myArray = [myArray; array]; I think you should read some documentation. F = repmat ( getframe ( hFig_cp ), 1, n_fr ); for fr = 1 : n_fr. field1Processing the last element first forces preallocation of the entire vector in the first hit, as the debugger confirms: unprocessedData = fetchData (); % note that processedData isn't declared outside the loop - this breaks % it if it'll later hold non-numeric data. head = struct ('number', cell (1, 10), 'pck_rv', cell (1, 10)); Now head is a [1 x 10] struct array withe the fields 'number' and 'pck_rv'. You could preallocate the structures inside. NET, and Python ® data structures to. C=cell (1,N) it is like you are creating N separate MATLAB variables except that they do not have distinct names (x,y,z, etc. 0. Even after that it is not giving me the results &. 0. My answer is a bit late, but there are a few things I'd mention regarding array growth and pre-allocation in MATLAB. This also makes it difficult to determine what size the two arrays should be. To preallocate the object array, assign the last element of the array first. my_struct_data. If this is the case, then set your. You can fill in each element in the array with a graphics object handle. NET, and Python ® data structures to. Learn more about empty value numeric matrix . Preallocate a 4-by-1 array: h = gobjects (4,1); Assign axes handles to the array elements: tiledlayout (2,2) for k=1:4 h (k) = nexttile; end. So any cell array and vector can be predeclared with, e. Use the appropriate preallocation function for the kind of array you want to initialize: zeros for numeric arrays strings for string arrays cell for cell arrays table for table arrays. You can fill in each element in the array with a graphics object handle. For categorical arrays, use the logical operators == or ~= to select data that is in, or not in, a particular category. Solutions to the problem. one should pre-allocate for a for loop which fills a matrix a zero matrix of the required size. This is because if you created Np copies of a list element using *, you get Np references to the same thing. I think the problem is that the fact that your string array is inside the field of a struct, instead of being a plain local variable, is defeating Matlab's "in-place update" optimization, so it's actually copying the entire array each time you update it, undoing your attempt to preallocate it. g. Theme. StructureName (1). 3. Preallocate Memory for Cell Array. names = cell (1,100); % approximately 100 names for the students in class. inside the loop. arrays with dtype=object are similar - arrays of pointers to objects such as lists. Do NOT use a cell array of structures, this just. arr = np. I've been trying A = zeros(50,50,50,50,50, 'uint8'); Which works to create one from 0-255 but I can't find what to write in the quotes to make it logical rather. Note that in your code snippet you are emptying the correlation = [] variable each time through the loop rather than just appending to it. many columns of data all of type double) so using for example sz =[1000,1000]; vartype = {'double','double',. Learn more about struct, structures, memory MATLAB How to preallocate 3 D matrix?.