On Mar 17, 2006, at 13:01 , Ann Gentile wrote:
> Hello,
>
> I would like to be able distinguish values that are invalid
> calling RRDs::fetch vs using rrdtool fetch. That is:
>
> at time 1142539176
>
> calling:
> rrdtool fetch "<myrrdhere>" AVERAGE -r 1 -e now -s e-1min
>
> returns:
>
> timestamp sum
>
> 1142539080: 2.3500000000e+01
> 1142539140: nan
> 1142539200: nan
This is two minutes.
The numerical results are: (NaN is 0 or infinity)
1142539080 23.5
1142539140 0.0
1142539200 0.0
>
>
> whereas using:
If you're on a POSIX system, Perl supports the "POSIX::strtod"
function. Its semantics are somewhat cumbersome, so here's a "getnum"
wrapper function for more convenient access. This function takes a
string and returns the number it found, or "undef" for input that
isn't a C float. The "is_numeric" function is a front end to "getnum"
if you just want to say, ``Is this a float?''
sub getnum {
use POSIX qw(strtod);
my $str = shift;
$str =~ s/^\s+//;
$str =~ s/\s+$//;
$! = 0;
my($num, $unparsed) = strtod($str);
if (($str eq '') || ($unparsed != 0) || $!) {
return undef;
} else {
return $num;
}
}
sub is_numeric { defined getnum($_[0]) }
> my ($start,$step,$names,$data) = RRDs::fetch ...
> foreach my $line (@$data) {
> print " ", scalar localtime($start), " ($start) ";
> $start += $step;
> foreach my $val (@$line) {
if (! is_numeric($val)) {
printf "$val"; # there's no number to return.
} else {
printf "%12.1f ", $val; # there's a number to return
}
> }
> print "\n";
> }
>
> prints out:
> 1142539080 23.5
> 1142539140 0.0
>
>
> Two questions:
> 1) Since at time 1142539176 rrdtool fetch returns
> nan for times 1142539140 & 1142539200, but later fills
> them in I assume that they are just not calculated yet, as
> opposed to nan results due to data points that will never
> come in -- is there a way to determine that this is the case ?
> 2) Is there someother way I can use RRDs::fetch to get back
> something other than 0.0 for the values that appear as nan
> when I call rrdtool fetch, since 0.0 may be a valid return
> value for my calculation?
It wasn't returning 0.0, you forced this with: printf "%12.1f ", $val;
> Thank you,
> Ann
>
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