In MATLAB how do I insert a string at beginning of of each string in a cell array?

问题

I have a cell array of numeric strings e.g.:

labels = {'1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11', '12'}

I'm trying to add a string ('Label ') to the beginning of each array element without using any kind of loop, as the array is massive and I need the code to run quickly. My other requirement is the space after the word 'Label' must be maintained once I apply it to the two-digit elements in the array. The result I want is:

fullLabels = {'Label 1', 'Label 2', 'Label 3', 'Label 4', 'Label 5',
              'Label 6', 'Label 7', 'Label 8', 'Label 9', 'Label 10',
              'Label 11', 'Label 12'}

I tried using strcat() like this:

fullLabels = strcat('Label ', labels);

This is fine for the single-digit array elements, but when it is applied to the two-digit array elements, the space after 'Label' is removed to give:

fullLabels = {..., 'Label10', 'Label11', 'Label12'}

回答1:

strcat trims trailing whitespace from all inputs prior to concatenation. You will want to manually concatenate the strings using [].

fullLabels = cellfun(@(x)['Label ', x], labels, 'UniformOutput', false)

%   'Label 1'
%   'Label 2'
%   'Label 3'
%   'Label 4'
%   'Label 5'
%   'Label 6'
%   'Label 7'
%   'Label 8'
%   'Label 9'
%   'Label 10'
%   'Label 11'
%   'Label 12'

You could also use something like regexprep to prepend the label. This replaces the first character of each label with itself (\1) with 'Label ' appended to the front.

fullLabels = regexprep(labels, '^.', 'Label \1')

Update

@Dev-iL's answer mentioned using a cell array to pass a space to strcat which I wasn't aware of. Rather than concatenating the space, we could also just stick 'Label ' inside the cell.

strcat({'Label '}, labels)

回答2:

Since strcat only removes trailing spaces, if you manage to get your number strings to begin with a space (using the settings of whatever converts them from "proper numbers"), you will not see this problem:

labels = {' 1', ' 2', ' 3', ' 4', ' 5', ' 6', ' 7', ' 8', ' 9', ' 10', ' 11', ' 12'};
fullLabels = strcat('Label',labels);

Alternatively, as mentioned here, you can "fool" strcat by surrounding the space with a cell:

fullLabels = strcat('Label', {' '}, labels);

来源：https://stackoverflow.com/questions/37998621/in-matlab-how-do-i-insert-a-string-at-beginning-of-of-each-string-in-a-cell-arra