#!/usr/bin/perl -w

############################  Grep and Map  #############################

opendir(D,".") or die "Cannot open current directory!\n";

@dirs = grep { -d } readdir D;
print "Directories under current dir: @dirs\n";
rewinddir D;

@bigger_than_10000_bytes = grep { -s > 10000 } readdir D;
print "Files > 10000 bytes: @bigger_than_10000_bytes\n";

rewinddir D;
@longnames = grep { length() >= 20} readdir D;
print "Filenames >= 20 characters: @longnames\n";

rewinddir D;
@three_hundred_lines = grep {open(F,"$_"),@lines = <F>,@lines >= 300} readdir D;
print "Files with >= 300 lines: @three_hundred_lines\n";

$dir = "$ENV{HOME}/inet/demos";
opendir(D, "$dir") or die "Cannot open internet demos!\n";
@bigger_than_40000_bytes = grep { -s > 40000 } map {"$dir/$_"} readdir D;
print "Files > 40000 bytes: @bigger_than_40000_bytes\n";
closedir D;

@decimals = qw(10 20 30 40 50);
@octals   = map {sprintf "%o", $_} @decimals;  # Three one-to-one mappings!
@hexes    = map {sprintf "%x", $_} @decimals;
@squares = map {$_ * $_} @decimals;
print "Octals: @octals\n";
print "Hexes:   @hexes\n";
print "Squares: @squares\n";

@strs = qw(foobar simple four on eighteen);
@two_chars = map {/../g} @strs;   # One-to-many mapping!
print "@two_chars\n";

#  grep -n emulation
open(F,"grep-map.pl") or die "Cannot open grep-map.pl!\n";
@matches = map {$lnum++; /print/ ? sprintf("%-5d: %s", $lnum, $_) : ()} <F>;
print @matches;  #  () takes up no element in @matches!!!

#  grep -c emulation
seek(F, 0, 0);
$count = grep {/print/} <F>;
print "$count\n";   #  Number of lines matching the pattern!!
                    #  Grep has a meaningful scalar context. Map doesn't!

@scores   = qw(75 65 63 80 97 87 67 76 97 97 84 90);
$high     = (sort {$a <=> $b} @scores)[-1];
$NumHighs = grep {$_ == $high} @scores;  #  How many people had the high score?
print "$NumHighs\n";

%scores = ("Doe,John" => 75, "Dover,Ben" => 65, "Wonka,Willie" => 63,
           "He,Ben"   => 80, "Smart,Tom" => 97, "Smith,Chris"  => 67,
           "Tal,Mike" => 76, "Yang,Yu"   => 97, "Sheth,Mia"    => 97,
           "Horn,Joe" => 84, "Larkin,Ed" => 90);

$HighScore = (sort {$a <=> $b} values %scores) [-1];
%Highs = map {$scores{$_} == $HighScore ? ($_, $scores{$_}) : ()} keys %scores;
foreach $name (keys %Highs) {print "$name $Highs{$name}\n"}

$x = [1,2,3,4];  #  A taste of the future ---> REFERENCES!!
$y = [3,4,5,6];
$z = [5,9,6,6];
@coordinates = map { [$x->[$_], $y->[$_], $z->[$_]] } 0..3;
foreach $listref (@coordinates)
{
     print "(@$listref)\n";
}
###############################  Program Output  ##############################

Directories under current dir: . ..

Files > 10000 bytes: .. bundle file.demo.16

Filenames >= 20 characters: index-substr.demo.18 random-access.demo.17

Files with >= 300 lines: bundle file.demo.16

Files > 40000 bytes: /mnt/diska/staff/perry/inet/demos/handouts

Octals: 12 24 36 50 62    #  One-to-one mappings
Hexes:   a 14 1e 28 32
Squares: 100 400 900 1600 2500

fo ob ar si mp le fo ur on ei gh te en   # One-to-many mappings via m/../g

# grep -n emulation
8    : print "Directories under current dir: @dirs\n";
13   : print "Files > 10000 bytes: @bigger_than_10000_bytes\n";
17   : print "Filenames >= 20 characters: @longnames\n";
21   : print "Files with >= 300 lines: @three_hundred_lines\n";
26   : print "Files > 40000 bytes: @bigger_than_40000_bytes\n";
30   : @octals   = map {sprintf "%o", $_} @decimals;  # Three one-to-one mappings!
31   : @hexes    = map {sprintf "%x", $_} @decimals;
33   : print "Octals: @octals\n";
34   : print "Hexes:   @hexes\n";
35   : print "Squares: @squares\n";
39   : print "@two_chars\n";
43   : @matches = map {$lnum++; /print/ ? sprintf("%-5d: %s", $lnum, $_) : ()} <F>;
44   : print @matches;  #  () takes up no element in @matches!!!
48   : $count = grep {/print/} <F>;
49   : print "$count\n";   #  Number of lines matching the pattern!!
55   : print "$NumHighs\n";
64   : foreach $name (keys %Highs) {print "$name $Highs{$name}\n"}
72   :      print "(@$listref)\n";

18  #  Result of grep -c emulation

3   #  Number of people with high score of 97

Sheth,Mia 97  # The hash of those people created via map.
Smart,Tom 97
Yang,Yu 97

(1 3 5)       # Result of map used to create [x,y,z] triplets
(2 4 9)
(3 5 6)
(4 6 6)