string join does not work for char arrays?

I have a column list of numbers like the below

M = [2; 3; 5; 7; 16];

What I want is to create a string array like this

"2, 3, 5, 7, 16"

Why can't I use the below to get what I want? What is the correct way to do this?

b = join(num2str(M), ', ')

Here is the error:

"First argument must be a string array, character vector, or cell array of character vectors."

Answer 1

[Star Strider]

One approach:

M = [2; 3; 5; 7; 16];
M2Str = sprintf("%d, ",M(1:end-1)) + string(M(end))

producing:

M2Str = 
    "2, 3, 5, 7, 16"

.

Answer 2

[Walter Roberson]

strjoin(string(M),', ')

or

strjoin(cellstr(num2str(M)),', ')

You could also consider

num2str(M.', '%g, ')

but that will leave an extra trailing comma

[Leon]

Many thanks! This is probably the cleanest way to do this.

Answer 3

[Steven Lord]

>> M = [2; 3; 5; 7; 16];
>> join(string(M), ", ")

ans = 

    "2, 3, 5, 7, 16"

num2str on M makes a char matrix which is not a "string array, character vector, or cell array of character vectors" and so is not a valid input to join. [Technically the error message should probably state 'character row vector', actually.]

[Leon]

Thank you. I didn't know it was as simple as that. I should use the function string instead of num2str.

Answer 4

[Jeremy Perez]

Hi Leon,

Type:

help num2str

> num2str: Convert numbers to character representation.

You're not using strings but character arrays, which are different datatypes in MATLAB.

Try not to use character arrays as much as possible when you mean to use strings.

You can use:

join(string(M), ', ')
strjoin(string(M), ', ')

You can also test this:

sprintf('%d, ', M)

It'll add a comma at the end of your string that you can remove but it's a very useful function.

[Leon]

Thanks for the tips!