This does most of the work for you, but I've left some things for you to do:
<DATA>;
my @prev_line;
while ( <DATA> ) {
my @this_line = split /[,\s]+/;
shift @this_line;
print join( ", ", map { "$this_line[$_]-$prev_line[$_]" } 0 .. $#t
+his_line ), "\n"
if @prev_line;
@prev_line = @this_line;
}
__DATA__
date, val1, val2, val3, val4
1/2/2007, 1, 4, 5, 6
1/3/2007, 2, 5, 7, 10
1/5/2007, 5, 6, 8, 11
Output:
2-1, 5-4, 7-5, 10-6
5-2, 6-5, 8-7, 11-10
You may find this version easier to follow (using the same __DATA__ as earlier):
<DATA>;
my @prev_line;
while ( <DATA> ) {
my @this_line = split /[,\s]+/;
shift @this_line;
if ( @prev_line ) {
my @output;
for ( 0 .. $#this_line ) {
push @output, "$this_line[$_]-$prev_line[$_]";
}
print join( ", ", @output ), "\n";
}
@prev_line = @this_line;
}
That leaves you with the job and handling the files.
I'm sure google will help, and there's always the Perl documentation.
update: omitted __DATA__ first time round
update^2: added second example
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