Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ames!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: variable is numeric?
Message-ID: <7449@jpl-devvax.JPL.NASA.GOV>
Date: 17 Mar 90 02:59:13 GMT
References: <16918@orstcs.CS.ORST.EDU> <7443@jpl-devvax.JPL.NASA.GOV> <16943@orstcs.CS.ORST.EDU>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 92

In article <16943@orstcs.CS.ORST.EDU> pvo@sapphire.OCE.ORST.EDU (Paul O'Neill) writes:
: A lot of survey data comes through this lab.  Data from different institutions
: using different instruments in different formats.  Some is in feet that needs
: converting to meters.
: 
: Almost invariably, the data needing conversion appear as a triplet of
: numbers.  What a great job for perl!
: 
: My perl script to convert surveyed feet to surveyed meters justs looks for
: a line w/ 3 consecutive numbers and multiplies all such triplets by
: 0.3048006.  
: 
: BUT IT'S UGLY:
: 
: -----------------------------------------------------------------------
: #!/usr/local/bin/perl
: #
: # ft2m_any.perl
: # 27 feb 90
: # Paul V. O'Neill -- Coastal Imaging Lab, OSU, Corvallis, OR 97331
: #
: # feet to meters convertion on lines consisting of 3 consecutive numbers
: # leave other lines alone
: #
: format STDOUT = 
:         @<<<<<<         @<<<<<<         @<<<<<<<
:         $meters[0],     $meters[1],     $meters[2]
: .
: 
: while (<>) {                            # get a line at a time
:     $save = $_;
:     @feet = /([0123456789.]*)\s*([0123456789.]*)\s*([0123456789.]*)\s*/;
:     if($feet[2]) {
:         @meters = grep($_ *= .304800609601, @feet );
:         write;
:     } else {
:         print $save;
:     }
: }
: --------------------------------------------------------------
: 
: [0123456789.]  seems a gross way to identify a number.  And "10.33.9" would
: pass the test.

You can say [0-9.].  Or [\d.]. 

If you're worried about multiple dots, I'd suggest \d*\.?\d+ or \d+\.?\d*.
Do you allow ".1" or only "0.1"?

: If perl knows that a variable is numeric (automagical increment writeup)
: why can't I know?  I'd much prefer to split the current line and do some
: cute, canonical test on each member of @_ for "numberness."

What's the matter with (assuming no leading .'s)

	@feet = grep(/^\d+\.?\d*$/,split(' '));
	if (@feet == 3) {		# found 3 numbers (patchlevel 12)

Or maybe, if your numbers are always greater than 0

	@feet = grep($_ + 0, split(' '));

Of course, if that's true, there's always

	if ($feet[0] * $feet[1] * $feet[2]) {

If they can be zero, how about

	@feet = grep($_ + 0 || /^0\.?0*$/, split(' '));

or

	@feet = grep($_ + 0 || /^0?\.?0+$/, split(' '));

Presuming your triples are on a line by themselves, and you don't care
much about how much whitespace or precision you end up with, you could
probably write your script as

	while (<>) {
	    @nums = grep((s/\.//,/^-?\d+$/), split(' '));
	    s/([\d.]+)/$1 * .304800609601/eg if @nums == 3;
	    print;
	}

I would try to avoid the write in any case:

        while (<>) {
            @meters = grep(/^0\.?0*$/ || $_ *= .304800609601, split(' '));
            $_ = sprintf("        %7.7s         %7.7s         %8.8s\n",@meters)
                if @meters == 3;
            print;
        }

This can be reduced to

	#!/usr/local/bin/perl -p
	@meters = grep(/^0\.?0*$/ || $_ *= .304800609601, split(' '));
	$_ = sprintf("        %7.7s         %7.7s         %8.8s\n",@meters)
	    if @meters == 3;

In general, perl never knows whether your string looks like a number,
because it just assumes it's a number and forces the issue whenever you
treat it like a number.  It would be wasting CPU to do otherwise.
Seeing that your variable != 0 is at least indicative that the front
of the string looked like a non-zero number.  Other than than, you have
to be explicit.

Larry