WJP I find large numbers hard to read without group delimiters, but Tcl's format command doesn't provide automatic delimiter insertion the way some recent versions of C printf do. Here's a Tcl procedure that does the job. It defaults to a group size of 3 and comma as the delimiter but has optional arguments that allow other choices for locales that use other delimiters and group sizes.
See also commas added to numbers.
# Given a number represented as a string, insert delimiters to break it up for
# readability. Normally, the delimiter will be a comma which will be inserted every
# three digits. However, the delimiter and groupsize are optional arguments,
# permitting use in other locales.
#
# The string is assumed to consist of digits, possibly preceded by spaces,
# and possibly containing a decimal point, i.e.: [:space:]*[:digit:]*\.[:digit:]*
proc DelimitNumber {number {delim ","} {GroupSize 3}} {
# First, extract right hand part of number, up to and including decimal point
set point [string last "." $number];
if {$point >= 0} {
set PostDecimal [string range $number $point end];
set PostDecimalP 1;
} else {
set point end;
set PostDecimal "";
set PostDecimalP 0;
}
# Now extract any leading spaces.
set ind 0;
while {[string equal [string index $number $ind] \u0020]} {
incr ind;
}
set FirstNonSpace $ind;
set LastSpace [expr $FirstNonSpace - 1];
set LeadingSpaces [string range $number 0 $LastSpace];
# Now extract the non-fractional part of the number, omitting leading spaces.
set MainNumber [string range $number $FirstNonSpace $point];
# Insert commas into the non-fractional part.
set Length [string length $MainNumber];
set Phase [expr $Length % $GroupSize]
set PhaseMinusOne [expr $Phase -1];
set DelimitedMain "";
#First we deal with the extra stuff.
if {$Phase > 0} {
append DelimitedMain [string range $MainNumber 0 $PhaseMinusOne];
}
set FirstInGroup $Phase;
set LastInGroup [expr $FirstInGroup + $GroupSize -1];
while {$LastInGroup < $Length} {
if {$FirstInGroup > 0} {
append DelimitedMain $delim;
}
append DelimitedMain [string range $MainNumber $FirstInGroup $LastInGroup];
incr FirstInGroup $GroupSize
incr LastInGroup $GroupSize
}
# Reassemble the number.
if {$PostDecimalP} {
return [format "%s%s.%s" $LeadingSpaces $DelimitedMain $PostDecimal];
} else {
return [format "%s%s" $LeadingSpaces $DelimitedMain];
}
}