### Re^2: Read Only Error -- Sorting an Array

by perlstudent89 (Initiate)
 on Sep 18, 2012 at 02:50 UTC ( #994173=note: print w/replies, xml ) Need Help??

Your solution with grep is the one I eventually used. With the map implementation, I was throwing away the '0' numerals. Do you know why that is?

I interpreted map {\$_ ? \$_ : ()} as saying, this such that this is whitespace. So then, why is it throwing away '0'? And length \$_ solves this by keeping things that have a length? Since '0' has length of 1 but '' hasn't a length..?

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Re^3: Read Only Error -- Sorting an Array
by tobyink (Abbot) on Sep 18, 2012 at 06:56 UTC
```map { \$_ ? \$_ : () }

means (if we pretend that there's a built-in function is_true()) the same as:

```map {
if (is_true(\$_)) {
\$_;
}
else {
();
}
}

In Perl, there are five things that are considered false: undef, the empty string, the number zero (including when written 0e0, 0.0, etc), the string "0" (but not strings like "0e0" or "0.0") and objects which overload conversion to boolean to return false.

The zeros passing through your map are false, thus go down the "else" path.

So we don't want to test is_true; we want to test whether each string has any characters... i.e. a non-zero length:

```map { length(\$_) ? \$_ : () }

Any any map which ends with ?\$_:() should probably be a grep:

```grep { length(\$_) }
perl -E'sub Monkey::do{say\$_,for@_,do{(\$monkey=[caller(0)]->[3])=~s{::}{ }and\$monkey}}"Monkey say"->Monkey::do'
Thanks for your thought out reply. Writing in Perl is becoming much easier thanks to you!

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