Averages/Arithmetic mean: Difference between revisions

=={{header|Standard ML}}==

These functions return a real:

<lang sml>fun mean_reals [] = 0.0

| mean_reals xs = foldl op+ 0.0 xs / real (length xs);

val mean_ints = mean_reals o (map real);</lang>

the previous code is easier to read and understand, though if you which

the fastest implementation to use in production code notice several points:

it is possible to save a call to <code>length</code> computing the length through

the <code>foldl</code>, and for mean_ints it is possible to save calling

<code>real</code> on every numbers, converting only the result of the addition.

Also the task asks to return 0 on empty lists, but in Standard ML this case

would rather be handled by an exception.

<lang sml>fun mean_reals [] = raise Empty

| mean_reals xs = let

val (total, length) =

foldl

(fn (x, (tot,len)) => (x + tot, len + 1.0))

(0.0, 0.0) xs

in

(total / length)

end;

fun mean_ints [] = raise Empty

| mean_ints xs = let

val (total, length) =

foldl

(fn (x, (tot,len)) => (x + tot, len + 1.0))

(0, 0.0) xs

in

(real total / length)

end;

</lang>