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matlabstrcat
stanigator
stanigator

Reputation: 10944

Matlab strcat function troubles with spaces

I'm trying to accomplish this:

strcat('red ', 'yellow ', 'white ')

I expected to see "red yellow white", however, I see "redyellowwhite" on the command output. What needs to be done to ensure the spaces are concatenated properly? Thanks in advance.

Upvotes: 32

Views: 41171

Answers (5)

Andrew Janke
Andrew Janke

Reputation: 23908

You can protect trailing whitespace in strcat() or similar functions by putting it in a cell.

str = strcat({'red '}, {'yellow '}, {'white '})
str = str{1}

Not very useful in this basic example. But if you end up doing "vectorized" operations on the strings, it's handy. Regular array concatenation doesn't do the 1-to-many concatenation that strcat does.

strs = strcat( {'my '}, {'red ','yellow ','white '}, 'shirt' )

Sticking 'my ' in a cell even though it's a single string will preserve the whitespace. Note you have to use the {} form instead of calling cellstr(), which will itself strip trailing whitespace.

This is all probably because Matlab has two forms of representing lists of strings: as a cellstr array, where all whitespace is significant, and as a blank-padded 2-dimensional char array, with each row treated as a string, and trailing whitespace ignored. The cellstr form most resembles strings in Java and C; the 2-D char form can be more memory efficient if you have many strings of similar length. Matlab's string manipulation functions are polymorphic on the two representations, and sometimes exhibit differences like this. A char literal like 'foo' is a degenerate one-string case of the 2-D char form, and Matlab's functions treat it as such.

UPDATE: As of Matlab R2019b or so, Matlab also has a new string array type. Double-quoted string literals make string arrays instead of char arrays. If you switch to using string arrays, it will solve all your problems here.

Upvotes: 13

Kevin_Hu
Kevin_Hu

Reputation: 161

In fact, you can simply use the ASCII code of space: 32. So, you can solve the problem like this:

str = strcat('red', 32, 'yellow', 32, 'white');

Then you will get str = 'red yellow white'.

Upvotes: 16

gnovice
gnovice

Reputation: 125874

Although STRCAT ignores trailing white space, it still preserves leading white space. Try this:

strcat('red',' yellow',' white')

Alternatively, you can just use the concatenation syntax:

['red ' 'yellow ' 'white ']

Upvotes: 24

Amro
Amro

Reputation: 124563

or you can say:

str = sprintf('%s%s%s', 'red ', 'yellow ', 'white ')

Upvotes: 2

nsanders
nsanders

Reputation: 12656

From the matlab help page for strcat:

"strcat ignores trailing ASCII white space characters and omits all such characters from the output. White space characters in ASCII are space, newline, carriage return, tab, vertical tab, or form-feed characters, all of which return a true response from the MATLAB isspace function. Use the concatenation syntax [s1 s2 s3 ...] to preserve trailing spaces. strcat does not ignore inputs that are cell arrays of strings. "

Upvotes: 23

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