In Julia, Insert Commas Into Integers For Printing Like Python 3.6+

I want to insert commas into large integers for printing. julia> println(123456789) # Some kind of flag/feature inserts commas. '123,456,789' In Python 3.6+ this is easy to do

Solution 1:

I guess the most straightforward way in some languages would be to use the ' format modifier in printf. I Julia this WOULD look like so:

using Printf # a stdlib that ships with julia which defines @printf@printf"%'d"12345678

However, unfortunately, this flag is not yet supported as you can see from the error you'll get:

julia> @printf "%'d"12345678
ERROR: LoadError: printfformat flag ' not yet supported

If you like this feature, maybe you should think about adding it to the Printf stdlib so that everyone would benefit from it. I don't know how difficult this would be though.

UPDATE: Note that although the macro is defined in stdlib Printf, the error above is explicitly thrown in Base/printf.jl:48. I also filed an issue here

Solution 2:

Here is a function based on a Regex from "Regular Expressions Cookbook," by Goyvaerts and Levithan, O'Reilly, 2nd Ed, p. 402, that inserts commas into integers returning a string.

functioncommas(num::Integer)
    str = string(num)
    returnreplace(str, r"(?<=[0-9])(?=(?:[0-9]{3})+(?![0-9]))" => ",")
endprintln(commas(123456789))
println(commas(123))
println(commas(123456789123456789123456789123456789))

""" Output
123,456,789
123
123,456,789,123,456,789,123,456,789,123,456,789
"""