#### How do I convert strings to floating number?

```Hi there,

I have a simple problem that I'm sure has been asked before (so why not
again ;))

I have a list like this:

1e-100
2e-100
1e-45
5e-10
1
10
20

and want to make correct assignments:

1e-100	SMALL
2e-100	SMALL
1e-45	BIGGER
5e-10	BIGGER
1	BIGGER
10	BIG
20	BIG

But with this code

while (<>) {
chomp;
if (\$_ lt 1e-50) {
print "\$_\t SMALL\n";
} elsif ((\$_ gt 1e-50) && \$_ lt 5) {
print "\$_\t BIGGER\n";
} elsif (\$_ gt 5) {
print "\$_\t BIGGEST\n";
}

I only get

1e-100   SMALL
2e-100   BIGGER
1e-45    SMALL
5e-10    BIGGEST
1        SMALL
10       SMALL
20       BIGGER

which is not matematically correct. How do convert "floating strings" to
floating number? I thought "lt" would be the right one to choose...

Marcus

```
 0
m
10/14/2003 11:24:26 AM
perl.beginners 29360 articles. 3 followers.

6 Replies
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```Marcus Claesson wrote:

> Hi there,
>
> I have a simple problem that I'm sure has been asked before (so why not
> again ;))
>
> I have a list like this:
>
> 1e-100
> 2e-100
> 1e-45
> 5e-10
> 1
> 10
> 20
>
> and want to make correct assignments:
>
> 1e-100  SMALL
> 2e-100  SMALL
> 1e-45   BIGGER
> 5e-10   BIGGER
> 1       BIGGER
> 10      BIG
> 20      BIG
>
> But with this code
>
> while (<>) {
>     chomp;
>     if (\$_ lt 1e-50) {
>         print "\$_\t SMALL\n";
>     } elsif ((\$_ gt 1e-50) && \$_ lt 5) {
>         print "\$_\t BIGGER\n";
>     } elsif (\$_ gt 5) {
>         print "\$_\t BIGGEST\n";
>     }

lt, gt etc. are used for string comparisons. Change 'lt' to < and 'gt' to >

>
>
> I only get
>
> 1e-100   SMALL
> 2e-100   BIGGER
> 1e-45    SMALL
> 5e-10    BIGGEST
> 1        SMALL
> 10       SMALL
> 20       BIGGER
>
> which is not matematically correct. How do convert "floating strings" to
> floating number? I thought "lt" would be the right one to choose...
>
> Marcus

```
 0
sraghavan
10/14/2003 11:44:05 AM
```> lt, gt etc. are used for string comparisons. Change 'lt' to < and 'gt' to >
> and your code should work.
>

You're right, but this script was a simplification of a bigger one where
'>' didn't work (my mistake to not spot the difference...). Here is a
more 'real' situation:

Input file:
4635a   1e-180  BL0976
4635a   0       BL0978
4635a   1e-10   BL1343
4635a   8e-86   BL1774
4635a   6e-18   Blon1206
4635a   1e-123  BL1165
4635a   5       BL0978
4635a   50      BL0978

Script:

while (<>) {
@row = (split /\t/);
(\$contig,\$E_value,\$locus_tag) = (@row);
if (\$E_value < 1e-50) {
print "\$E_value\t SMALL\n";
} elsif ((\$E_value > 1e-50) && \$E_value < 5) {
print "\$E_value\t BIGGER\n";
} elsif (\$_ > 5) {
print "\$E_value\t BIGGEST\n";
}
}

And I then get this:
1e-180   SMALL
0        SMALL
1e-10    BIGGER
8e-86    SMALL
6e-18    BIGGER
1e-123   SMALL
Argument "\x{34}\x{36}..." isn't numeric in numeric gt (>) at
/home/marcus/Scripts/string2num.pl line 7, <> line 7.
5        BIGGEST
Argument "\x{34}\x{36}..." isn't numeric in numeric gt (>) at
/home/marcus/Scripts/string2num.pl line 7, <> line 8.
50       BIGGEST

Thus, the operator isn't always correct and is not very accepted by perl

Do you know the error?

Marcus

```
 0
m
10/14/2003 12:04:26 PM
```Marcus Claesson said:
> Hi there,
>
> I have a simple problem that I'm sure has been asked before (so why not
> again ;))
>
> I have a list like this:
>
> 1e-100
> 2e-100
> 1e-45
> 5e-10
> 1
> 10
> 20
>
> and want to make correct assignments:
>
> 1e-100	SMALL
> 2e-100	SMALL
> 1e-45	BIGGER
> 5e-10	BIGGER
> 1	BIGGER
> 10	BIG
> 20	BIG
>
> But with this code
>
> while (<>) {
>     chomp;
>     if (\$_ lt 1e-50) {
>         print "\$_\t SMALL\n";
>     } elsif ((\$_ gt 1e-50) && \$_ lt 5) {
>         print "\$_\t BIGGER\n";
>     } elsif (\$_ gt 5) {
>         print "\$_\t BIGGEST\n";
>     }
>
> I only get
>
> 1e-100   SMALL
> 2e-100   BIGGER
> 1e-45    SMALL
> 5e-10    BIGGEST
> 1        SMALL
> 10       SMALL
> 20       BIGGER
>
> which is not matematically correct. How do convert "floating strings" to
> floating number? I thought "lt" would be the right one to choose...

You don't need to.  If you want it to be a number, use it like one.  That
means using < and > instead of lt and gt.

You'll also probably want <= or >= at some points in case you get 1e-50
and 5 as input.

--
Paul Johnson - paul@pjcj.net
http://www.pjcj.net

```
 0
paul
10/14/2003 12:05:16 PM
```Marcus Claesson wrote:
> > lt, gt etc. are used for string comparisons. Change 'lt' to < and
> > 'gt' to > and your code should work.
> >
>
> You're right, but this script was a simplification of a
> bigger one where
> '>' didn't work (my mistake to not spot the difference...). Here is a
> more 'real' situation:
>
> Input file:
> 4635a   1e-180  BL0976
> 4635a   0       BL0978
> 4635a   1e-10   BL1343
> 4635a   8e-86   BL1774
> 4635a   6e-18   Blon1206
> 4635a   1e-123  BL1165
> 4635a   5       BL0978
> 4635a   50      BL0978
>
> Script:
>
> while (<>) {
>     @row = (split /\t/);
>     (\$contig,\$E_value,\$locus_tag) = (@row);
>     if (\$E_value < 1e-50) {
>         print "\$E_value\t SMALL\n";
>     } elsif ((\$E_value > 1e-50) && \$E_value < 5) {
>         print "\$E_value\t BIGGER\n";
>     } elsif (\$_ > 5) {

This should be referencing \$E_value, not \$_.

>         print "\$E_value\t BIGGEST\n";
>     }
> }

This whole thing should be simplified:

while(<>) {
my (\$contig,\$E_value,\$locus_tag) = split;
if (\$E_value < 1e-50) {
print "\$E_value\t SMALL\n";
} elsif (\$E_value < 5) {
print "\$E_value\t BIGGER\n";
} else {
print "\$E_value\t BIGGEST\n";
}
}

>
> And I then get this:
> 1e-180   SMALL
> 0        SMALL
> 1e-10    BIGGER
> 8e-86    SMALL
> 6e-18    BIGGER
> 1e-123   SMALL
> Argument "\x{34}\x{36}..." isn't numeric in numeric gt (>) at
> /home/marcus/Scripts/string2num.pl line 7, <> line 7. 5        BIGGEST
> Argument "\x{34}\x{36}..." isn't numeric in numeric gt (>) at
> /home/marcus/Scripts/string2num.pl line 7, <> line 8. 50       BIGGEST
>
> Thus, the operator isn't always correct and is not very
> accepted by perl

The operator is correct. Your program has a bug.
```
 0
Bob_Showalter
10/14/2003 1:13:14 PM
```Marcus Claesson wrote:

> > lt, gt etc. are used for string comparisons. Change 'lt' to < and 'gt' to >
> > and your code should work.
> >
>
> You're right, but this script was a simplification of a bigger one where
> '>' didn't work (my mistake to not spot the difference...). Here is a
> more 'real' situation:
>
> Input file:
> 4635a   1e-180  BL0976
> 4635a   0       BL0978
> 4635a   1e-10   BL1343
> 4635a   8e-86   BL1774
> 4635a   6e-18   Blon1206
> 4635a   1e-123  BL1165
> 4635a   5       BL0978
> 4635a   50      BL0978
>
> Script:
>
> while (<>) {
>     @row = (split /\t/);
>     (\$contig,\$E_value,\$locus_tag) = (@row);
>     if (\$E_value < 1e-50) {
>         print "\$E_value\t SMALL\n";
>     } elsif ((\$E_value > 1e-50) && \$E_value < 5) {
>         print "\$E_value\t BIGGER\n";
>     } elsif (\$_ > 5) {

I think you meant elsif (\$E_value > 5) {
You might also want to add a >= or <= somewhere to process 5 or 1e-50

>
>         print "\$E_value\t BIGGEST\n";
>     }
> }
>

```
 0
sraghavan
10/14/2003 1:15:22 PM
```>>>>> "Marcus" == Marcus Claesson <m.claesson@student.ucc.ie> writes:

Marcus> while (<>) {
Marcus>     chomp;
Marcus>     if (\$_ lt 1e-50) {

Don't use "lt" for numbers.  Use "<".

--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
Perl/Unix/security consulting, Technical writing, Comedy, etc. etc.
See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training!
```
 0
merlyn
10/14/2003 3:02:45 PM

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