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As you saw, 6.25 are closer to 6 than to 7 because 25% along the set of
the twelve numbers is closer to the third number (6) than to he fourth
(7). The median (50-percentile) is also really interpolated, but it is
always in the middle of the two center numbers if there are an even count
of numbers.

However, there is two methods of interpolation:

Example, we have only three numbers: 5, 6 and 7.

Method 1: The most common is to say that 5 and 7 lays on the 25- and
75-percentile. This method is used in Acme::Tools.

Method 2: In Oracle databases the least and greatest numbers
always lay on the 0- and 100-percentile.

As an argument on why Oracles (and others?) definition is not the best way is to
look at your data as for instance temperature measurements.  If you
place the highest temperature on the 100-percentile you are sort of
saying that there can never be a higher temperatures in future measurements.

Tools.pm  view on Meta::CPAN

 10  1          17.00

If the first argument is a coderef, that sub will be called for each permutation and the return from those calls with be the real return from C<permutations()>. For example this:

 print for permutations(sub{join"",@_},1..3);

...will print the same as:

 print for map join("",@$_), permutations(1..3);

...but the first of those two uses less RAM if 3 has been say 9.
Changing 3 with 10, and many computers hasn't enough memory
for the latter.

The examples prints:

 123
 132
 213
 231
 312
 321

If you just want to say calculate something on each permutation,
but is not interested in the list of them, you just don't
take the return. That is:

 my $ant;
 permutations(sub{$ant++ if $_[-1]>=$_[0]*2},1..9);

...is the same as:

 $$_[-1]>=$$_[0]*2 and $ant++ for permutations(1..9);