How do I add commas to numbers using fprintf?

Hello,

How do I add commas to numbers using fprintf? My customer wants me to write out tables and have commas in the numbers to better read it. For instance, 123456789.0 would be written out as 123,456,789.0. Thanks.

Best regards,

Bill Rooker

Answer 1

[Stephen23]

fprintf cannot do that, but you will find several FEX submissions that can create a string with commas as thousands separators:

https://www.mathworks.com/matlabcentral/fileexchange/52832-num2sepstr

https://www.mathworks.com/matlabcentral/fileexchange/41520-insert-commas-into-numbers

If you read the comments to those submissions you will also find several improvements to consider.

Another easy one-line approach:

str = ["1234567890.123456789";"-1234567890";"0"]

str = 3×1 string array
    "1234567890.123456789"
    "-1234567890"
    "0"

str = regexprep(str,'(?<!(\.|[eE][-+]?)\d*)\d{1,3}(?=(\d{3})+(e|E|\.|\>))','$&,')

str = 3×1 string array
    "1,234,567,890.123456789"
    "-1,234,567,890"
    "0"

[Bill Rooker]

Thank you!

[Dyuman Joshi]

@Stephen23, could you recommend some good resources for learning the use of regexp() and regexprep() in MATLAB?

[Stephen23]

The only resources I really use are the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html

https://www.mathworks.com/help/matlab/matlab_prog/dynamic-regular-expressions.html

https://www.mathworks.com/help/matlab/matlab_prog/lookahead-assertions-in-regular-expressions.html

etc.

You can find some online tutorials etc that explain regular expression concepts** but these often are based on Perl or JavaScript or Python or whatever regular expressions (i.e. not the same details) so once you really need to know the details then the only place to look is the MATLAB documentation. Be prepared to read those pages many times.

If you want to experiment then you might find this useful:

https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-tool

** as well as many websites offering all kinds of automagic things with regular expressions.

[Dyuman Joshi]

I tried working with the documentation pages of regexp() and regexprep(), but haven't been successful with it, as they are not clear/specific enough to me and do not provide sufficient examples to understand the functionality properly.

Thank you very much for the links, I didn't know about these pages, they are what I was looking for!

I have also tried a few online tutorials, but as you mentioned, the functionality of regexp() in other languages are different than in MATLAB.

I will also look into the FEX submission you have link, it does look very extensive, but for now, I will start from the basics with the documentation pages you linked.

Once again, Thank you!

Answer 2

[Ted Shultz]

you can do this in two lines. from this page : A simple way is to add this two line function:

function numOut = addComma(numIn)
   jf=java.text.DecimalFormat; % comma for thousands, three decimal places
   numOut= char(jf.format(numIn)); % omit "char" if you want a string out
end

Hope that helps! --ted

[Roscoe Cook]

Worked great for me! Perhaps this should be the accepted answer. Thanks!

[Stargaet]

very good! thanks!

[Kouichi C. Nakamura]

Thanks! Extended it to 2d matrix.

function B = AddCommaArr(A)

B = strings(size(A));

for i = 1:size(A,1)
    for j = 1:size(A,2)
        
        B(i,j) = addComma(A(i,j));
    end
end

function numOut = addComma(numIn)
   jf=java.text.DecimalFormat; % comma for thousands, three decimal places
   numOut= char(jf.format(numIn)); % omit "char" if you want a string out
end

end

[Daven Gooden]

@Ted Shultz: Spot on! Very clean and easy to understand/use! Thank you very mutch!

[Edwin Cortez]

Great ! Thanks

Answer 3

[Jim Svensson]

I feel that in 2021 this functionality should be supported by sprintf/fprintf.

[Jim Svensson]

I feel that in 2023 this functionality should be supported by sprintf/fprintf.

[Dyuman Joshi]

@Jim Svensson If you want to have a functionality implemented in MATLAB, you can raise a feature request for it.

https://in.mathworks.com/matlabcentral/answers/460998-how-can-i-make-a-features-request

I believe you will need a strong justification to convince TMW as to why they should implement it.

[Image Analyst]

It would certainly be a convenience if they had a letter to do that conversion, like p or whatever (some unused letter), like

x = 12345678.912345
fprintf('Number = %p.\n', x);

'12,345,678.912'

Answer 4

[Image Analyst]

See my attached utility function that inserts commas to make a string out of a number. Then in your fprintf you print the string with %s instead of %d or %f. For example:

number = 1234567;
fprintf('The number is %s.\n', CommaFormat(number));

The number is 1,234,567.

Answer 5

[Toshiaki Takeuchi]

Using pattern

vec = 123456789;
txt = string(vec);
pat1 = lookBehindBoundary(digitsPattern); % (?<=\d)
pat2 = asManyOfPattern(digitsPattern(3),1); % (\d{3})+
pat3 = lookAheadBoundary(pat2+lineBoundary("end")); % (?=(\d{3})+$)
pat4 = pat1+pat3; % (?<=\d)(?=(\d{3})+$)
replace(txt,pat4,",") 

ans = "123,456,789"

[Stephen23]

vec = 1234.56789

vec = 1.2346e+03

txt = string(vec);
pat1 = lookBehindBoundary(digitsPattern); % (?<=\d)
pat2 = asManyOfPattern(digitsPattern(3),1); % (\d{3})+
pat3 = lookAheadBoundary(pat2+lineBoundary("end")); % (?=(\d{3})+$)
pat4 = pat1+pat3; % (?<=\d)(?=(\d{3})+$)
replace(txt,pat4,",") 

ans = "1234.5,679"