Aha. The problem here is
*how do I implement a parser to process a table of data based on a user
supplied query*
Ok, look at the following:-
#!/usr/bin/perl
use strict; - matter of style
use warnings; - and again
# This DATASET has the following columns, with these names in this
order.
my @col = qw( x1 x2 x3 y1 y2 y3 y4 );
# Fabricate a set of functions (subs) in the 'filter' name space which
parallel
# the column names, and enchant each with the ability to look up a data
element.
# Note the use of 'my $i=$_' This tweaks some magic in perl and causes
the automatically
# generated functions to be *closures* and not just normal functions.
map{ my $i=$_; no strict 'refs'; *{"filter::$col[$i]"} = sub{$_->[$i]} }
0..$#col;
# This is your data set. If you want 'line number as the first col
remember to add it to
# '@col' above.
my @data=(
[qw( 0.200000 0.200000 0.200000 0.765685 75881.9
29289.3 -46592.6)],
[qw( 0.200345 0.200000 0.200345 0.966661 75766.0
29268.4 -46497.6)],
[qw( 0.200000 0.200345 0.200000 0.766030 75867.1
29259.8 -46607.4)],
[qw( 0.359575 0.253987 0.359575 1.271019 43898.7
19675.6 -24223.1)],
[qw( 0.359921 0.253987 0.359921 1.271995 43861.3
19666.1 -24195.2)]
);
# Perform filtering. First parameter is a $coderef which is passed to
GREP for the
# actual filtering task.
sub filterdata($@)
{
my $cref=shift;
grep &$cref,@_
}
# Build the coderef for the specified data filter. The (only) parameter
is the
# text string 'x1 > 5' etc.
sub filterspec
{
my $e = shift;
map{ $e =~ s/\b$_\b/filter::$_()/g } @col;
eval "sub{ $e }"
}
# Here goes.......
# I want to filter according to the following spec:
my $expr = "x1 > 0.2 && x1 < 0.3 && y1 > 0.8 && y3 > 15000 && y3 <
30000";
# Compile the spec into a handler... The DIE will catch errors compiling
the filter.
# This usually occurs because you do silly things, call non-existent
functions, or
# use column names which don't exist.
my $filter_handler = filterspec( $expr ) or die $@;
# Perform the filter using the handler.
my @result = filterdata $filter_handler,@data;
# Display the table of results.
print join("$/",map{join(" ",@$_)[EMAIL PROTECTED]).$/;
This outputs one row:
0.200345 0.200000 0.200345 0.966661 75766.0 29268.4 -46497.6
Now remember. I fiddled the data and expression so they that WOULD match
one line. Your sample data matched nothing.
How does this help? I'm sorry if it is less readable than the specific
implementation of a particular filter.
------------------------------------------------------------------------
----------------------------------
Thanks Mr.David for the response.
I want the same logic in a generalized manner, because the conditions
keep changing as the data changes. Also in each condition string, the
delimiters can be anything (like <, >, <=, >=, or =). Hence I would
like to have a more generalized way.
Your solution has given me a way to think further ahead. Further help in
this regard is solicited.
Thanks
Regards
Guruguhan
EACoE, India.
-----Original Message-----
From: David le Blanc [mailto:[EMAIL PROTECTED]
Sent: Monday, February 16, 2004 6:34 PM
To: N, Guruguhan (GEAE, Foreign National, EACOE); [EMAIL PROTECTED]
Subject: RE: data filtering
Guruguhan,
Can I assume you have the data in memory?
Can I further assume the data is contained in an array of arrays?
Can I also further assume that the conditions you mentioned are AND'd?
(ie
the final result is the intersection of all conditions?)
Thus $data[0][0] = 0.200000 (aka, X1 from row 1)
Consider the following: (purposely written in readable perl)
my @filtered = ();
for( @data ){
push @filtered,$_ if
$$_[0] > 0.2 && $$_[0] < 0.3 && # 0.2 < x1 < 0.3
$$_[3] > 0.8 && # y1 > 0.8
$$_[5] > 15000 && $$_[5] < 30000; # 15000 < y3 < 30000
}
[EMAIL PROTECTED] data contains filtered result result.
Is that what you were thinking of?
Regards,
David le Blanc
--
Senior Technical Specialist
I d e n t i t y S o l u t i o n s
Level 1, 369 Camberwell Road, Melbourne, Vic 3124
Ph 03 9813 1388 Fax 03 9813 1688 Mobile 0417 595 550
Email [EMAIL PROTECTED]
-----Original Message-----
From: N, Guruguhan (GEAE, Foreign National, EACOE)
[mailto:[EMAIL PROTECTED]
Sent: Monday, 16 February 2004 10:47 PM
To: [EMAIL PROTECTED]
Subject: data filtering
Hi All,
I have a data set ( only a portion) as follows:
No. x1 x2 x3 y1 y2 y3
y4
1 0.200000 0.200000 0.200000 0.765685 75881.9 29289.3
-46592.6
2 0.200345 0.200000 0.200345 0.766661 75766.0 29268.4
-46497.6
3 0.200000 0.200345 0.200000 0.766030 75867.1 29259.8
-46607.4
4 0.359575 0.253987 0.359575 1.271019 43898.7 19675.6
-24223.1
5 0.359921 0.253987 0.359921 1.271995 43861.3 19666.1
-24195.2
This data set has to be filtered using the following conditions (
example only. in reality this can be anything):
0.2 < x1 < 0.3
y1 > 0.8
15000 < y3 < 30000
I have to filter the data set satisfying all the conditions.
Can somebody help me out to do the same. Any help in this regard is
solicited.
Thanks
Regards
Guruguhan
EACoE, India.
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