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>
