Problem with the use of strrep command

I have a problem with strrep command. I have noticed that this command no use for cell array with square bracket character ([])

Could you please help me?

[Voss]

What do you mean by a "cell array with square bracket character"?

Show an example where strrep doesn't work as expected.

[Askic V]

Here is one example with cell array with square brackets and use of strrep function:

aa = {['first'],['second']}

aa = 1×2 cell array
    {'first'}    {'second'}

aa

aa = 1×2 cell array
    {'first'}    {'second'}

aa(1) = strrep(aa(1),'first','replacement');
aa

aa = 1×2 cell array
    {'replacement'}    {'second'}

Can you explain what problem could be here?

[DGM]

In that case, the square brackets have no influence over the processing.

aa = {['first'],['second']}

is the same as

aa = {'first','second'}

Since we're guessing here, other interpretations might include:

% an unintended concatenation
aa = {['first','second']}

... or

% the brackets are within the char vectors
aa = {'first [subexpr]','second [other subexpr]'}

Where either the brackets themselves are to be replaced (shouldn't be a problem), or the subexpressions therin are to be replaced (strrep would be the wrong tool).

Alternatively, my guess is that this might not even be a cellchar

% a cell of strings or string arrays might cause problems
aa = {"first" "second"}
aa = {["first" "second"]}

in which case the solution really depends on what's in the cell array, how it's arranged, and whether it should even be in a cell array.

But we'll have to wait.

Answer 1

[Steven Lord]

That is correct, when called with a cell array with some char vectors in the cells as input strrep requires each element of that cell array to be a char vector. I'm using try / catch here so I can run code after the section that throws the error.

a = {'apple', [], 'cherry'}

a = 1×3 cell array
    {'apple'}    {0×0 double}    {'cherry'}

try
    strrep(a, 'e', 'E')
catch ME
    fprintf("This call threw error '%s'.\n", ME.message)
end

This call threw error 'Cell elements must be character vectors.'.

Use cellfun or a for loop to replace the empty numeric elements with an empty char array.

E = cellfun(@isempty, a);
a(E) = {''}

a = 1×3 cell array
    {'apple'}    {0×0 char}    {'cherry'}

strrep(a, 'e', 'E')

ans = 1×3 cell array
    {'applE'}    {0×0 char}    {'chErry'}

[DGM]

Ohh I didn't even think about having an empty vector in the mix!

[Askic V]

Cool, thank you for the insight @Steven Lord.

Important thing to watch for!

[Steven Lord]

More likely than not the code that generated the variable a did not explicitly assigned an empty vector into it, so it's easy to overlook that possibility.

a = {'apple'}

a = 1×1 cell array
    {'apple'}

a{3} = 'cherry'

a = 1×3 cell array
    {'apple'}    {0×0 double}    {'cherry'}

MATLAB needed to put something into the second cell in the variable a when I assigned 'cherry' into the third cell. It essentially chose []. In this case where I knew I wanted all the cells to have text data I might have preallocated the cell array with repmat to ensure all cells had some text data. That's not so much preallocating for memory (cells in a cell array are not required to be contiguous in memory like elements in a numeric array) but more preallocating with the expected types.

b = repmat({''}, 1, 3)

b = 1×3 cell array
    {0×0 char}    {0×0 char}    {0×0 char}

b{1} = 'apple'

b = 1×3 cell array
    {'apple'}    {0×0 char}    {0×0 char}

b{3} = 'cherry'

b = 1×3 cell array
    {'apple'}    {0×0 char}    {'cherry'}

strrep(b, 'e', 'E')

ans = 1×3 cell array
    {'applE'}    {0×0 char}    {'chErry'}