Provided by: libsort-fields-perl_1.001-3_all 
NAME
Sort::Fields - Sort lines containing delimited fields
SYNOPSIS
use Sort::Fields;
@sorted = fieldsort [3, '2n'], @lines;
@sorted = fieldsort '\+', [-1, -3, 0], @lines;
$sort_3_2n = make_fieldsort [3, '2n'], @lines;
@sorted = $sort_3_2n->(@lines);
DESCRIPTION
Sort::Fields provides a general purpose technique for efficiently sorting lists of lines
that contain data separated into fields.
Sort::Fields automatically imports two subroutines, "fieldsort" and "make_fieldsort", and
two variants, "stable_fieldsort" and "make_stable_fieldsort". "make_fieldsort" generates
a sorting subroutine and returns a reference to it. "fieldsort" is a wrapper for the
"make_fieldsort" subroutine.
The first argument to make_fieldsort is a delimiter string, which is used as a regular
expression argument for a "split" operator. The delimiter string is optional. If it is
not supplied, make_fieldsort splits each line using "/\s+/".
The second argument is an array reference containing one or more field specifiers. The
specifiers indicate what fields in the strings will be used to sort the data. The
specifier "1" indicates the first field, "2" indicates the second, and so on. A negative
specifier like "-2" means to sort on the second field in reverse (descending) order. To
indicate a numeric rather than alphabetic comparison, append "n" to the specifier. A
specifier of "0" means the entire string ("-0" means the entire string, in reverse order).
The order in which the specifiers appear is the order in which they will be used to sort
the data. The primary key is first, the secondary key is second, and so on.
"fieldsort [1, 2], @data" is roughly equivalent to "make_fieldsort([1, 2])->(@data)".
Avoid calling fieldsort repeatedly with the same sort specifiers. If you need to use a
particular sort more than once, it is more efficient to call "make_fieldsort" once and
reuse the subroutine it returns.
"stable_fieldsort" and "make_stable_fieldsort" are like their "unstable" counterparts,
except that the items that compare the same are maintained in their original order.
EXAMPLES
Some sample data (in array @data):
123 asd 1.22 asdd
32 ewq 2.32 asdd
43 rewq 2.12 ewet
51 erwt 34.2 ewet
23 erww 4.21 ewet
91 fdgs 3.43 ewet
123 refs 3.22 asdd
123 refs 4.32 asdd
# alpha sort on column 1
print fieldsort [1], @data;
123 asd 1.22 asdd
123 refs 3.22 asdd
123 refs 4.32 asdd
23 erww 4.21 ewet
32 ewq 2.32 asdd
43 rewq 2.12 ewet
51 erwt 34.2 ewet
91 fdgs 3.43 ewet
# numeric sort on column 1
print fieldsort ['1n'], @data;
23 erww 4.21 ewet
32 ewq 2.32 asdd
43 rewq 2.12 ewet
51 erwt 34.2 ewet
91 fdgs 3.43 ewet
123 asd 1.22 asdd
123 refs 3.22 asdd
123 refs 4.32 asdd
# reverse numeric sort on column 1
print fieldsort ['-1n'], @data;
123 asd 1.22 asdd
123 refs 3.22 asdd
123 refs 4.32 asdd
91 fdgs 3.43 ewet
51 erwt 34.2 ewet
43 rewq 2.12 ewet
32 ewq 2.32 asdd
23 erww 4.21 ewet
# alpha sort on column 2, then alpha on entire line
print fieldsort [2, 0], @data;
123 asd 1.22 asdd
51 erwt 34.2 ewet
23 erww 4.21 ewet
32 ewq 2.32 asdd
91 fdgs 3.43 ewet
123 refs 3.22 asdd
123 refs 4.32 asdd
43 rewq 2.12 ewet
# alpha sort on column 4, then numeric on column 1, then reverse
# numeric on column 3
print fieldsort [4, '1n', '-3n'], @data;
32 ewq 2.32 asdd
123 refs 4.32 asdd
123 refs 3.22 asdd
123 asd 1.22 asdd
23 erww 4.21 ewet
43 rewq 2.12 ewet
51 erwt 34.2 ewet
91 fdgs 3.43 ewet
# now, splitting on either literal period or whitespace
# sort numeric on column 4 (fractional part of decimals) then
# numeric on column 3 (whole part of decimals)
print fieldsort '(?:\.|\s+)', ['4n', '3n'], @data;
51 erwt 34.2 ewet
43 rewq 2.12 ewet
23 erww 4.21 ewet
123 asd 1.22 asdd
123 refs 3.22 asdd
32 ewq 2.32 asdd
123 refs 4.32 asdd
91 fdgs 3.43 ewet
# alpha sort on column 4, then numeric on the entire line
# NOTE: produces warnings under -w
print fieldsort [4, '0n'], @data;
32 ewq 2.32 asdd
123 asd 1.22 asdd
123 refs 3.22 asdd
123 refs 4.32 asdd
23 erww 4.21 ewet
43 rewq 2.12 ewet
51 erwt 34.2 ewet
91 fdgs 3.43 ewet
# stable alpha sort on column 4 (maintains original relative order
# among items that compare the same)
print stable_fieldsort [4], @data;
123 asd 1.22 asdd
32 ewq 2.32 asdd
123 refs 3.22 asdd
123 refs 4.32 asdd
43 rewq 2.12 ewet
51 erwt 34.2 ewet
23 erww 4.21 ewet
91 fdgs 3.43 ewet
BUGS
Some rudimentary tests now.
Perhaps something should be done to catch things like:
fieldsort '.', [1, 2], @lines;
'.' translates to "split /./" -- probably not what you want.
Passing blank lines and/or lines containing the wrong kind of data (alphas instead of
numbers) can result in copious warning messages under "-w".
If the regexp contains memory parentheses ("(...)" rather than "(?:...)"), split will
function in "delimiter retention" mode, capturing the contents of the parentheses as well
as the stuff between the delimiters. I could imagine how this could be useful, but on the
other hand I could also imagine how it could be confusing if encountered unexpectedly.
Caveat sortor.
Not really a bug, but if you are planning to sort a large text file, consider using
sort(1). Unless, of course, your operating system doesn't have sort(1).
AUTHOR
Joseph N. Hall, "<joseph@5sigma.com>"
SEE ALSO
perl(1).