Last number in the array --- access problem --Newbie question

[Go Perl]

Here is the complete problem:
I have two files MAER_FILE and EVAL_FILE
MAER_FILE contains

ITR Max_error Avg_error Min_error
1 0.849197022974602 0.845806355744732 0.843444019245762
2 0.844939386865682 0.841991065818245 0.837942476416068
3 0.844144961481595 0.841099932356234 0.836919185707587
4 0.844144961481595 0.841099932356234 0.836919185707587
5 0.840596405164578 0.838883453436171 0.836919185707587
6 0.839512137681004 0.838072896555497 0.836534486876684

I have to get the last number of the 4th column which is
0.836534486876684 and so i use the following code.
#------
open (MAER_FILE, "MAER_output.txt");
while (<MAER_FILE>) {
chomp;
my @maer_array = split(/\t/);
print "$maer_array[-1]\n";
}
#------

But this gives me the output as the entire 4th column instead of just
the last number.
once i get the last number which is 0.836534486876684 i have to search
for this number in EVAL_FILE which looks like
ITR CHR SUM Error Error(%)
0 1 46.7058362636031 0.849197022974602 84.9197022974602
0 2 47.0231420611022 0.854966219292767 85.4966219292767
0 3 46.4794258296669 0.845080469630308 84.5080469630308
0 4 46.6549049902152 0.848270999822095 84.8270999822095
0 5 46.8269040494763 0.851398255445024 85.1398255445024
0 6 46.9823066656241 0.854223757556801 85.4223757556801
0 7 46.3894210585169 0.843444019245762 84.3444019245762
0 8 46.4279728814877 0.844144961481595 84.4144961481595
0 9 46.4266047910362 0.844120087109749 84.4120087109749

The last number in the previous line must match with one of the number
in the 4 th column of the above file and i should be able to extract
the entire line.
I am not able to store these columns into arrays..either i don't know
perl or arrays. Please help me solve this problem efficiently.
Thanks in advance,
GP

[Tore Aursand]

Go Perl wrote:

> ITR Max_error Avg_error Min_error
> 1 0.849197022974602 0.845806355744732 0.843444019245762
> 2 0.844939386865682 0.841991065818245 0.837942476416068
> 3 0.844144961481595 0.841099932356234 0.836919185707587
> 4 0.844144961481595 0.841099932356234 0.836919185707587
> 5 0.840596405164578 0.838883453436171 0.836919185707587
> 6 0.839512137681004 0.838072896555497 0.836534486876684
>
> I have to get the last number of the 4th column which is
> 0.836534486876684 and so i use the following code.
> #------
> open (MAER_FILE, "MAER_output.txt");
> while (<MAER_FILE>) {
> chomp;
> my @maer_array = split(/\t/);
> print "$maer_array[-1]\n";
> }
> #------

As one should expect, this prints out the last columns for every row.
From what I understand, you just want the last column for the last row?
In that case, you should first get the last row, then the last column
for that row;

my @rows = <MAER_FILE>;
my $last = $rows[-1];
my @cols = split( /\s+/, $last );

The code above is just an example of how you should think. The actual
solution might differ a little; you should seriously think about how big
the file you're reading is, as 'my @rows = <MAER_FILE>;' throws the
whole file into memory.

> once i get the last number which is 0.836534486876684 i have to search
> for this number in EVAL_FILE which looks like
>
> [...]

> ITR CHR SUM Error Error(%)
> 0 1 46.7058362636031 0.849197022974602 84.9197022974602
> 0 2 47.0231420611022 0.854966219292767 85.4966219292767
> 0 3 46.4794258296669 0.845080469630308 84.5080469630308
> 0 4 46.6549049902152 0.848270999822095 84.8270999822095
> 0 5 46.8269040494763 0.851398255445024 85.1398255445024
> 0 6 46.9823066656241 0.854223757556801 85.4223757556801
> 0 7 46.3894210585169 0.843444019245762 84.3444019245762
> 0 8 46.4279728814877 0.844144961481595 84.4144961481595
> 0 9 46.4266047910362 0.844120087109749 84.4120087109749
>
> The last number in the previous line must match with one of the number
> in the 4 th column of the above file and i should be able to extract
> the entire line.

Hmm. I'm not quite sure if I understood that one. Do you mean that
your 'Min_Error' number from the MAER_FILE should match with one of the
'Error' numbers in the EVAL_FILE, and that the whole line with the match
should be printed out?

If that's the case:

my $wanted = 0.0;
open( MAER_FILE, 'maer.log' ) || die $! . "\n";
while ( <MAER_FILE> ) {
chomp;
$wanted = ( split(/\s+/) )[-1];
}
close( MAER_FILE );

open( EVAL_FILE, 'eval.log' ) || die $! . "\n";
while ( <EVAL_FILE> ) {
chomp;
if ( m,$wanted, ) {
print , "\n";
}
}
close( EVAL_FILE );

This is _totally_ untested, but you should get the idea. Feel free to
optmize the code when you figure out that the above works for you. :-)


--
Tore Aursand <tore@extend.no>

"I'm so old they've cancelled my blood type." -- Bob Hope

[Tad McClellan]

Go Perl <puissant00@yahoo.com> wrote:

> I have two files MAER_FILE and EVAL_FILE
> MAER_FILE contains
>
> ITR Max_error Avg_error Min_error
> 1 0.849197022974602 0.845806355744732 0.843444019245762

> my @maer_array = split(/\t/);

> But this gives me the output as the entire 4th column instead of just
> the last number.

I showed you how to solve that problem 3 days ago, so why are
you asking it yet again?

> which looks like
> ITR CHR SUM Error Error(%)
> 0 1 46.7058362636031 0.849197022974602 84.9197022974602
> 0 2 47.0231420611022 0.854966219292767 85.4966219292767

> I am not able to store these columns into arrays..

Do it using split() like you did for the other file.


--
Tad McClellan SGML consulting
[email]tadmc@augustmail.com[/email] Perl programming
Fort Worth, Texas

[Jay Tilton]

[email]puissant00@yahoo.com[/email] (Go Perl) wrote:

: I have two files MAER_FILE and EVAL_FILE
: MAER_FILE contains
:
: ITR Max_error Avg_error Min_error
: 1 0.849197022974602 0.845806355744732 0.843444019245762
: 2 0.844939386865682 0.841991065818245 0.837942476416068
[truncated]
:
: I have to get the last number of the 4th column which is
: 0.836534486876684

$want = (split /\t/, (grep 1+chomp, <MAER_FILE>)[-1])[-1];

: once i get the last number which is 0.836534486876684 i have to search
: for this number in EVAL_FILE which looks like
: ITR CHR SUM Error Error(%)
: 0 1 46.7058362636031 0.849197022974602 84.9197022974602
: 0 2 47.0231420611022 0.854966219292767 85.4966219292767
[truncated]
:
: The last number in the previous line must match with one of the number
: in the 4 th column of the above file and i should be able to extract
: the entire line.

($line) = grep {chomp; $want == (split /\t/)[3]} <EVAL_FILE>;

: I am not able to store these columns into arrays

Is creating such a data structure a necessary part of the solution?

: Please help me solve this problem efficiently.

What is your gauge of efficiency?

[Anno Siegel]

Tore Aursand <tore@aursand.no> wrote in comp.lang.perl.misc:

[...]

> From what I understand, you just want the last column for the last row?
> In that case, you should first get the last row, then the last column
> for that row;
>
> my @rows = <MAER_FILE>;
> my $last = $rows[-1];
> my @cols = split( /\s+/, $last );
>
> The code above is just an example of how you should think. The actual
> solution might differ a little; you should seriously think about how big
> the file you're reading is, as 'my @rows = <MAER_FILE>;' throws the
> whole file into memory.

The slurping can easily be avoided:

my $last;
$last = <MAER_FILE> until eof( MAER_FILE);

Or use File::ReadBackwards from CPAN.

Anno