How do I convert a numerical vector into a comma-delimited string?

Given a numerical vector, how do I convert it into a comma-delimited string?

For example, if

n = [12345 6789 10234 3452]

convert n to

12345,6789,10234,3452

Answer 1

[D.W. Frye]

n = [12345 6789 10234 3452];
allOneString = sprintf('%.0f,' , n);
allOneString = allOneString(1:end-1);% strip final comma

Answer 2

[Michael]

Have another one-liner:

regexprep(num2str(n),'\s+',',')

If uninitiated in the secrets of (Matlab's) regular expressions: \s stands for any whitespace and the + means 1 or more times. This is needed because the amount of space between the numbers output by num2str varies depending on the length of those numbers.

Answer 3

[EvilDrW]

here's another answer, but is a one liner

strjoin(arrayfun(@(x) num2str(x),n,'UniformOutput',false),',')

Answer 4

[Jan Siegmund]

Here is another oneliner:

strjoin(cellstr(num2str(n')),',')

Testing all four types with a script

n = randi(100,[1 100]);
tic;
s1 = sprintf('%.0f,' , n);
s1 = s1(1:end-1);
toc
tic;
s2 = strjoin(arrayfun(@(x) num2str(x),n,'UniformOutput',false),',');
toc
tic;
s3 = regexprep(num2str(n),'\s+',',');
toc
tic;
s4 = strjoin(cellstr(num2str(n')),',');
toc

deliveres:

Elapsed time is 0.000248 seconds.
Elapsed time is 0.005549 seconds.
Elapsed time is 0.000746 seconds.
Elapsed time is 0.003352 seconds.

The accepted answer is the fastest.

Answer 5

[Dyuman Joshi]

(Quite) A simple approach that has not been mentioned yet -

n = [12345 6789 10234 3452];
out = strjoin(string(n),",")

out = "12345,6789,10234,3452"

[Dyuman Joshi]

It is also the fastest -

%Testing with larger values
n = randi([1e3 1e4],[1 100]);
tic;
s1 = sprintf('%.0f,' , n);
s1 = s1(1:end-1);
t(1)=toc;

tic;
s2 = strjoin(arrayfun(@(x) num2str(x),n,'UniformOutput',false),',');
t(2)=toc;

tic;
s3 = regexprep(num2str(n),'\s+',',');
t(3)=toc;

tic;
s4 = strjoin(cellstr(num2str(n')),',');
t(4)=toc;

tic;
s5 = strjoin(string(n),',');
t(5)=toc;

t

t = 1×5

0.0122 0.0069 0.0049 0.0092 0.0025

isequal(s1,s2,s3,s5)

ans = logical
   1

s4 gives a different output, something with space and all (I'll elaborate tomorrow, it's 3 am here rn)

[Bruno Luong]

The first method is not optimal with format '%.0f', for integer better using '%i' (method 6)

n = randi([1e3 1e4],[1 1000]);
t = zeros(1,6);

t(1) = timeit(@() csnum1(n), 1);
t(2) = timeit(@() csnum2(n), 1);
t(3) = timeit(@() csnum3(n), 1);
t(4) = timeit(@() csnum4(n), 1);
t(5) = timeit(@() csnum5(n), 1);
t(6) = timeit(@() csnum6(n), 1);

tms = t*1e3

tms = 1×6

0.3778 8.9497 0.6823 4.0327 0.2052 0.2428

function s1 = csnum1(n)
s1 = sprintf('%.0f,' , n);
s1 = s1(1:end-1);
end

function s2 = csnum2(n)
s2 = strjoin(arrayfun(@(x) num2str(x),n,'UniformOutput',false),',');
end

function s3 = csnum3(n)
s3 = regexprep(num2str(n),'\s+',',');
end

function s4 = csnum4(n)
s4 = strjoin(cellstr(num2str(n')),',');
end

function s5 = csnum5(n)
s5 = strjoin(string(n),',');
end

function s = csnum6(n)
s = sprintf('%i,' , n);
s = s(1:end-1);
end

[Dyuman Joshi]

Even after the change, Method 6 is (marginally) slower than Method 5 (which is the fastest).

Answer 6

[RST]

We can also use compose() for a formatted one-liner:

a = rand(5,1);
csva = strjoin(compose('%.3f', a), ', ')

csva = '0.580, 0.062, 0.627, 0.295, 0.318'

and also for 2D arrays:

b = rand(3,4);
csvb = strjoin(join(compose( '%.3f', b), ', '), newline())

csvb = 
    '0.364, 0.708, 0.070, 0.747
     0.627, 0.454, 0.729, 0.557
     0.389, 0.398, 0.066, 0.471'

Answer 7

[Gianfranco Di Domenico]

EDIT: The backspace character is handled differently according to the final "usage" of the string. For instance, it works perfectly when displaying the string in the terminal; however, printing the string to a file does not remove the comma. Moreover, the byte array corresponding to the string retains both the comma and the backspace character.

More elegant, one liner:

n = [12345 6789 10234 3452]

n = 1×4

12345 6789 10234 3452

n_str = sprintf("%s\b", sprintf("%i,", n))

n_str = "12345,6789,10234,3452"

The logic:

• The nested sprintf creates a string of comma-separated values, but has a trailing comma
• The top-level sprintf prints the generated strings and the \b character (backspace) removes the trailing comma

[Bruno Luong]

Interesting.

It looks fine when displayed on screen but the internal string has 2 extra chararters of code 44 ',' and 8 backspash at the end. Not sure what side effect it has when precessing later.

n = [12345 6789]

n = 1×2

12345 6789

n_str = sprintf("%s\b", sprintf("%i,", n))

n_str = "12345,6789"

double(char(n_str))

ans = 1×12

49 50 51 52 53 44 54 55 56 57 44 8

[Gianfranco Di Domenico]

I just noticed this behavior.

I will edit the original answer because it seems that the behavior depends on the final usage of the string. For instance, fprintf-ing to a file does NOT work! The comma is retained.

[Bruno Luong]

Example

n = [12345 6789 10234 3452]

n = 1×4

12345 6789 10234 3452

n_str = sprintf("%s\b", sprintf("%i,", n))

n_str = "12345,6789,10234,3452"

str2num(n_str) % oh oh ...

ans =

     []

str2num(extractBefore(n_str,strlength(n_str)-1))

ans = 1×4

12345 6789 10234 3452

This might create some frustration and pain of debugging