Averages/Arithmetic mean

Write a program to find the mean (arithmetic average) of a numeric vector. The program should work on a zero-length vector (with an answer of 0).

J

mean=: +/ % #

That is, sum divided by the number of items. The verb also works on higher-ranked arrays. For example:

   mean 3 1 4 1 5 9
3.83333
   mean $0         NB. $0 is a zero-length vector
0
   x=: 20 4 ?@$ 0  NB. a 20-by-4 table of random (0,1) numbers
   mean x
0.58243 0.402948 0.477066 0.511155

The computation can also be written as a loop. It is shown here for comparison only and is highly non-preferred compared to the version above.

mean1=: 3 : 0
 z=. 0
 for_i. i.#y do. z=. z+i{y end.
 z % #y
)
   mean1 3 1 4 1 5 9
3.83333
   mean1 $0
0
   mean1 x
0.58243 0.402948 0.477066 0.511155

Java

Assume the numbers are in a double array called "nums".

...
double mean = 0;
double sum = 0;
for(double i : nums){
  sum += i;
}
System.out.println("The mean is: " + ((nums.length != 0) ? (sum / nums.length) : 0));
...

Perl

sub avg(@_) {
  $count = 0;
  $sum = 0;
  foreach (@_) {
    $sum += $_;
    $count++;
  }
  return $count > 0 ? $sum / $count : 0;
}

print avg(qw(3 1 4 1 5 9))."\n";

Output:

3.83333333333333

With module Data::Average. (For zero-length array returns ().)

use Data::Average;

my $d = Data::Average->new;
$d->add($_) foreach (qw(3 1 4 1 5 9));
print $d->avg."\n"

Output:

3.83333333333333