MATLAB concatenate string variables

Question

I know strjoin can be used to concatenate strings, like 'a' and 'b' but what if one of the strings is a variable, like

a=strcat('file',string(i),'.mat')

and I want:

strjoin({'rm',a})

MATLAB throws an error when I attempt this, and it's driving me crazy!

Error using strjoin (line 53) First input must be a string array or cell array of character vectors

Why not just use strcat again? strjoin is, per the documentation, for joining strings contained in an array. — sco1
– sco1, Commented Apr 20, 2018 at 2:14
RE: your edit, MATLAB's string and char classes are not the same. Per strcat's documentation, if any input is a string, then the output is a string, so a is a string. 'rm' is not a string, it's a character vector, so the cell array you edited in is not a cell array of character vectors. I don't agree with MATLAB's unyielding differentiation of string and char, but the error message is sufficiently explanatory. strcat('rm', a) still works fine. — sco1
– sco1, Commented Apr 20, 2018 at 14:07

matlabbit · Accepted Answer · 2018-04-20 04:54:03Z

5

What version of MATLAB are you using? What is the error? The first input to strjoin needs to be a cell array. Try strjoin({'rm'},a).

Also, before 17a, do:

a = strcat('file', num2str(i),'.mat')

In >=17a do:

a = "file" + i + ".mat";

Here is a performance comparison:

function profFunc

    tic;
    for i = 1:1E5
        a = strcat('file', num2str(i),'.mat');
    end
    toc;

    tic;
    for i = 1:1E5
        a = "file" + i + ".mat";
    end
    toc;
end

>> profFunc
Elapsed time is 6.623145 seconds.
Elapsed time is 0.179527 seconds.

edited Apr 20, 2018 at 4:54

answered Apr 20, 2018 at 4:48

matlabbit

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1 Comment

user3433489 Over a year ago

Thank you! I didn't realize I could use '+' in recent versions

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