whos - I can't capture the output

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dormant
dormant 2024-1-19
评论： Star Strider 2024-1-22
I need to debug a script that has memory issues. So I decided to use whos to print out the largest variables while it is running.
The option to store the output in a cell array doesn't seem to work for the workspace, as illustrated by the following:
>> whos
Name Size Bytes Class Attributes
C 5x1 572 cell
S 7x1 9852 struct
ans 1x102 204 char
datimNow 1x20 40 char
mem 1x105 210 char
memory 1x81 162 char
status 1x1 8 double
>> S = whos()
S =
7×1 struct array with fields:
name
size
bytes
class
global
sparse
complex
nesting
persistent
Am I doing something wrong, or is there a better way to monitor variable space use during execution?
  2 个评论
dormant
dormant 2024-1-19
OOps, I forgot to mention I am on Linux, so can't use the memory function.
Dyuman Joshi
Dyuman Joshi 2024-1-19
编辑：Dyuman Joshi 2024-1-19
"The option to store the output in a cell array doesn't seem to work for the workspace"
Maybe I am misunderstanding, but the outptut is a struct array.
You can get the data from the size field, corresponding to the variables in the name field.
Edit - Note that calling whos() multiple times in your code will lead to reduction in code efficiency.
From this particular documentation page- "Avoid functions that query the state of MATLAB such as inputname, which, whos, exist(var), and dbstack. Run-time introspection is computationally expensive."
@dormant, How many times is whos() called in your code? And do you just have to see which variable takes the most bytes for storage?

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采纳的回答

Star Strider
Star Strider 2024-1-19
Ran in:
Perhaps something like this —
A = magic(7);
B = string(randi(9, 4));
C = sin(2*pi*(0:0.01:1));
whos
Name Size Bytes Class Attributes A 7x7 392 double B 4x4 960 string C 1x101 808 double cmdout 1x33 66 char
S = whos;
Fields = fieldnames(S);
Contents = struct2cell(S);
whos_result = [cell2table(Fields) cell2table(Contents)]
whos_result = 9×5 table
Fields Contents1 Contents2 Contents3 Contents4 ______________ ____________ ____________ ____________ ____________ {'name' } {'A' } {'B' } {'C' } {'cmdout' } {'size' } {[ 7 7]} {[ 4 4]} {[ 1 101]} {[ 1 33]} {'bytes' } {[ 392]} {[ 960]} {[ 808]} {[ 66]} {'class' } {'double' } {'string' } {'double' } {'char' } {'global' } {[ 0]} {[ 0]} {[ 0]} {[ 0]} {'sparse' } {[ 0]} {[ 0]} {[ 0]} {[ 0]} {'complex' } {[ 0]} {[ 0]} {[ 0]} {[ 0]} {'nesting' } {1×1 struct} {1×1 struct} {1×1 struct} {1×1 struct} {'persistent'} {[ 0]} {[ 0]} {[ 0]} {[ 0]}
MemoryCell = whos_result(strcmp(whos_result.Fields,'bytes'), :)
MemoryCell = 1×5 table
Fields Contents1 Contents2 Contents3 Contents4 _________ _________ _________ _________ _________ {'bytes'} {[392]} {[960]} {[808]} {[66]}
Total_Variable_Memory_Used_Bytes = sum(cellfun(@sum, table2array(MemoryCell(:,2:end))))
Total_Variable_Memory_Used_Bytes = 2226
.
  2 个评论
Steven Lord
Steven Lord 2024-1-22
Ran in:
Rather than convert the struct into multiple cell arrays and displaying one table variable per workspace variable, I'd display one table row per workspace variable instead.
A = magic(7);
B = string(randi(9, 4));
C = sin(2*pi*(0:0.01:1));
T = struct2table(whos)
T = 4×9 table
name size bytes class global sparse complex nesting persistent __________ ________ _____ __________ ______ ______ _______ __________ __________ {'A' } 7 7 392 {'double'} false false false 1×1 struct false {'B' } 4 4 960 {'string'} false false false 1×1 struct false {'C' } 1 101 808 {'double'} false false false 1×1 struct false {'cmdout'} 1 33 66 {'char' } false false false 1×1 struct false
Then you can call whatever functions you want on the variables.
areAnyVariablesSparse = any(T.sparse)
areAnyVariablesSparse = logical
0
Note that simply summing up the bytes variable is not necessarily going to give you the total amount of memory used by MATLAB for those variables (copy-on-write, for example) but if you're looking for a quick approximation:
B = sum(T.bytes)
B = 2226
Star Strider
Star Strider 2024-1-22
@Steven Lord — Using struct2table is definitely more efficient. I don’t use struct arrays very often, so I didn’t consider using it.

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更多回答（2 个）

Hassaan
Hassaan 2024-1-19
The whos command by itself displays the information in the command window, but it doesn't return that information directly to a variable. To store this information in a variable, you need to use the evalin function with 'base' as the first argument, which evaluates the whos command in the base workspace and captures its output.
% Store the information about workspace variables in a struct array
workspaceVars = evalin('base', 'whos');
% Now you can process workspaceVars as needed
% For example, to display the names and sizes of the largest variables:
for i = 1:length(workspaceVars)
fprintf('Variable Name: %s, Size: %d bytes\n', workspaceVars(i).name, workspaceVars(i).bytes);
end
% You can sort them by size if you want to focus on the largest variables
[~, sortedIndices] = sort([workspaceVars.bytes], 'descend');
sortedVars = workspaceVars(sortedIndices);
% Display the sorted information
for i = 1:length(sortedVars)
fprintf('Variable Name: %s, Size: %d bytes\n', sortedVars(i).name, sortedVars(i).bytes);
end
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dormant
dormant 2024-1-22
Thank you to all answerers.
The problem turned out to be something that I could not diagnose with whois. The "culprit" was using mesh to plot a matrix that was far bigger than the screen resolution. That induced a memory overload and the system killed MATLAB.
I now decimate the matrix before plotting, and it seems to solve my problem.

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