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Manual Reference Pages  -  SORT::FIELDS (3)

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NAME

Sort::Fields - Sort lines containing delimited fields

CONTENTS

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).
Search for    or go to Top of page |  Section 3 |  Main Index


perl v5.20.3 FIELDS (3) 1998-01-30

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