David,Thanks much. I'll give it a shot and comeup with the code.
This is a new learning to me today :)
regards
-Ajey
On Sat, 23 Oct 2004, David le Blanc wrote:
> On Fri, 22 Oct 2004 20:13:05 -0700 (PDT), Ajey Kulkarni <[EMAIL PROTECTED]> wrote:
> > howdy!!
> > I've a code snipped that reads the file into array.
> > The file is a comma separated file. I want to say
> > get 4th column of the whole file in an array.
> >
> > @lines = LIB::readFile($opt{f});
> >
> > My @lines has the whole comma separated file.
> >
> > I would like to now get the 4th column of whole file (using @lines)
> > in an array. I can do this by parsing the @lines again ,split() and
> > get each array element,but this may be slow.
>
> This is difficult to optimise because perl doesn't have any way to
> pre-index a data structure in preparation for extracting data.
>
> Keep down the work by avoiding loop variables, iterate using internal
> functions and avoid splitting more than necessary.. Example:
>
> @lines = LIB::readfile(...);
>
> $col = 4;
> @coldata = map { (split(",",$_,$col+1))[$col] } @lines;
>
> Here, each element is spit into '$col + 1' columns, after all why split
> a data stream into 50 elements when you only want the fourth..
>
> The result of split is treated as an array, and the particular column [$col]
> is extracted.
>
> The result of the 'MAP' call is an array containing the fourth column of every
> line.
>
> Now, if you are going to do this more than once, you would split the whole file
> first, and then use two separate column extractions.
>
> Example:
>
> @lines = LIB::readfile(...);
>
> # Convert array of SCALARS to array of references to arrays of SCALARS.
> @line_data = map { [ split( ",", $_ ) ] } @lines;
>
> # Get col 3
> @col_3 = map { $_->[3] } @line_data;
>
> # Get col 7
> @col_7 = map { $_->[7] } @line_data;
>
> # - I use the $_->[x] syntax here because $$_[x] is ugly.
>
> HTH
> Cheers.
>
>
> >
> > Is there better way to achive this??
> >
> > Thanks a ton,
> > Ajey
> >
> > --
> > To unsubscribe, e-mail: [EMAIL PROTECTED]
> > For additional commands, e-mail: [EMAIL PROTECTED]
> > <http://learn.perl.org/> <http://learn.perl.org/first-response>
> >
> >
>
>
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
<http://learn.perl.org/> <http://learn.perl.org/first-response>
