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Idiom #173 Format a number with grouped thousands

Number will be formatted with a comma separator between every group of thousands.

s :: Int -> String
s = intersperseN ',' 3 . show

intersperseN :: a -> Int -> [a] -> [a]
intersperseN x n = uncurry (<>) . foldr alg ([], [])
  where
    alg a (buf', acc)
      | length buf >= n = ([], (x:buf) <> acc)
      | otherwise = (buf, acc)
      where buf = a:buf'
#define _POSIX_C_SOURCE 200809L
#include <locale.h>
#include <stdio.h>
setlocale(LC_ALL, "");
printf("%'d\n", 1000);
$"{1000:n}"
import std.format;
string f = "%3,d".format(123456);
import "golang.org/x/text/language"
import "golang.org/x/text/message"
p := message.NewPrinter(language.English)
s := p.Sprintf("%d\n", 1000)
new Intl.NumberFormat().format(1000);
import static java.lang.String.valueOf;
import static java.lang.System.out;
<N extends Number> String format(N n, char g, char d) {
    StringBuilder s = new StringBuilder();
    char a[] = valueOf(n).toCharArray();
    int i, m;
    for (i = 0, m = a.length; i < m; ++i)
        if (a[i] == d) {
            s.append(a, i, m - i);
            break;
        }
    while (i - 3 >= 0) {
        s.insert(0, a, i - 3, 3);
        if ((i = i - 3) > 0)
            s.insert(0, g);
    }
    s.insert(0, a, 0, i);
    return s.toString();
}
import static java.text.NumberFormat.getNumberInstance;
import java.text.DecimalFormat;
DecimalFormat f = (DecimalFormat) getNumberInstance();
f.setGroupingSize(3);
s = f.format(1000);
import java.text.DecimalFormat;
DecimalFormat decimalFormat = new DecimalFormat("#,###");
String formattedString = decimalFormat.format(1000000);
String.format("%,d", 1000000);
echo number_format(1000);
uses sysutils;
writeln(format('%.0n',[double(10000)]));   
 sub commify {
    local $_  = shift;
    1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
    return $_;
}
f'{1000:,}'
format(1000, ',')
'{:,}'.format(1000)
'1000'.gsub(/\B(?=(...)*\b)/, ',')
'1000'.reverse.scan(/.{1,3}/).join(',').reverse
require 'active_support/all'
1000.to_s(:delimited)
use separator::Separatable;
println!("{}", 1000.separated_string());
"%,d".format(n)
New implementation...
< > ⌨
cup 
s :: Int -> String
s = intersperseN ',' 3 . show

intersperseN :: a -> Int -> [a] -> [a]
intersperseN x n = uncurry (<>) . foldr alg ([], [])
  where
    alg a (buf', acc)
      | length buf >= n = ([], (x:buf) <> acc)
      | otherwise = (buf, acc)
      where buf = a:buf'
setlocale(LC_ALL, "");
printf("%'d\n", 1000);
$"{1000:n}"
string f = "%3,d".format(123456);
p := message.NewPrinter(language.English)
s := p.Sprintf("%d\n", 1000)
new Intl.NumberFormat().format(1000);
<N extends Number> String format(N n, char g, char d) {
    StringBuilder s = new StringBuilder();
    char a[] = valueOf(n).toCharArray();
    int i, m;
    for (i = 0, m = a.length; i < m; ++i)
        if (a[i] == d) {
            s.append(a, i, m - i);
            break;
        }
    while (i - 3 >= 0) {
        s.insert(0, a, i - 3, 3);
        if ((i = i - 3) > 0)
            s.insert(0, g);
    }
    s.insert(0, a, 0, i);
    return s.toString();
}
DecimalFormat f = (DecimalFormat) getNumberInstance();
f.setGroupingSize(3);
s = f.format(1000);
DecimalFormat decimalFormat = new DecimalFormat("#,###");
String formattedString = decimalFormat.format(1000000);
String.format("%,d", 1000000);
echo number_format(1000);
writeln(format('%.0n',[double(10000)]));   
 sub commify {
    local $_  = shift;
    1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
    return $_;
}
f'{1000:,}'
format(1000, ',')
'{:,}'.format(1000)
'1000'.gsub(/\B(?=(...)*\b)/, ',')
'1000'.reverse.scan(/.{1,3}/).join(',').reverse
1000.to_s(:delimited)
println!("{}", 1000.separated_string());
"%,d".format(n)