How to print an integer with a thousands separator in Matlab?

Question

I would like to turn a number into a string using a comma as a thousands separator. Something like:

x = 120501231.21;
str = sprintf('%0.0f', x);

but with the effect

str = '120,501,231.21' 

If the built-in fprintf/sprintf can't do it, I imagine cool solution could be made using regular expressions, perhaps by calling Java (which I assume has some locale-based formatter), or with a basic string-insertion operation. However, I'm not an expert in either Matlab regexp's or calling Java from Matlab.

Related question: How can I print a float with thousands separators in Python?

Is there any established way to do this in Matlab?

Answer 1

One way to format numbers with thousands separators is to call the Java locale-aware formatter. The "formatting numbers" article at the "Undocumented Matlab" blog explains how to do this:

>> nf = java.text.DecimalFormat;
>> str = char(nf.format(1234567.890123))

str =

1,234,567.89     

where the char(…) converts the Java string to a Matlab string.

voilà!

Answer 2

Here's the solution using regular expressions:

%# 1. create your formated string 
x = 12345678;
str = sprintf('%.4f',x)

str =
12345678.0000

%# 2. use regexprep to add commas
%#    flip the string to start counting from the back
%#    and make use of the fact that Matlab regexp don't overlap
%#    The three parts of the regex are
%#    (\d+\.)? - looks for any number of digits followed by a dot
%#               before starting the match (or nothing at all)
%#    (\d{3})  - a packet of three digits that we want to match
%#    (?=\S+)   - requires that theres at least one non-whitespace character
%#               after the match to avoid results like ",123.00"

str = fliplr(regexprep(fliplr(str), '(\d+\.)?(\d{3})(?=\S+)', '$1$2,'))

str =
12,345,678.0000