[Lemur]

Another one of my recent things I had to think for more than a few seconds about at work, summing an array collection.

Given an array collection:

[
  [1,2,3,4],
  [2,3,4,5],
  [3,4,5,6]
]

Return an array with the average of the columns:

[2,3,4,5]

While basic, you may find an interesting feature of Ruby.

Bonus

That same solution has to work for:

[[1,2,3,4]]

I'll post my solution some time later tomorrow, unless a lot of replies come in tonight.

Problem Sets

10 x 10

[
 [99, 47, 80, 22, 83, 45, 4, 4, 59, 65],
 [13, 24, 50, 86, 6, 72, 83, 46, 94, 96],
 [75, 73, 0, 56, 7, 50, 56, 49, 7, 56],
 [78, 28, 6, 44, 63, 0, 88, 88, 67, 45],
 [63, 70, 2, 7, 7, 71, 91, 66, 4, 78],
 [96, 38, 46, 90, 40, 50, 94, 53, 45, 31],
 [24, 37, 53, 19, 94, 11, 82, 12, 96, 84],
 [94, 7, 10, 71, 44, 15, 42, 72, 54, 95],
 [3, 13, 32, 30, 53, 58, 63, 76, 50, 11],
 [75, 8, 97, 68, 27, 4, 67, 98, 64, 1]
]

Solution:

[62, 34, 37, 49, 42, 37, 67, 56, 54, 56]

This post has been edited by Lemur: 27 January 2014 - 09:25 PM

[andrewsw]

What's a flattened average? Perhaps it has an alternative name as I couldn't discover it on a brief search.

[jon.kiparsky]

Here's a cute way to do it. Probably not canonical, but it works.

some_array_collection.reduce(:+).reduce(:+)

Probably this repetitive code will make someone cry...

(and yes, I know this isn't a general solution... working on that)

andrewsw, on 27 January 2014 - 08:54 PM, said:

What's a flattened average? Perhaps it has an alternative name as I couldn't discover it on a brief search.

Flatten the nested array, then take the average. "Flatten" is a typical FP function, it generally means to take a nested collection and return the inorder traversal.

(((this is) (a) deeply) (nested ((((collection))))) isn't it?)

=>flattens to=>

(this is a deeply nested collection, isn't it?)  

EDIT:
Okay, here's my better attempt:

some_nested_array.flatten.reduce(:)/>/>

Should have looked in the docs.

This post has been edited by jon.kiparsky: 27 January 2014 - 07:13 PM

[Lemur]

....it's a Monday. Rephrased to sum of columns.

[jon.kiparsky]

Note to self: read problem before solving. />

This post has been edited by jon.kiparsky: 27 January 2014 - 07:22 PM

[andrewsw]

Doh, on a quick read I was looking across the row at 1,2,3 then wondering why you were back-tracking to cover 2,3,4(?). It didn't help that these were the same numbers going down .. you could have gone all the way up-to 12

[Lemur]

To make it more fun, here are your generators:

def gen_row(n)
  n.times.reduce([]) { |ary, _| ary << rand(100).to_i }  
end  

def gen_table(n)
  n.times.reduce([]) { |ary, _| ary << gen_row(n) }
end

def rand_table
  gen_table(rand(100).to_i)
end

Make something that will get the average of each column for rand_table, which will be a 1x1 to 100x100 table with random numbers from 1 to 100.

Spoiler

def col_avg(table)
  table.transpose.reduce([]) { |ary, row| ary << (row.reduce(:+) / row.length) }
end

If I had known about transpose an hour earlier...

This post has been edited by Lemur: 27 January 2014 - 09:27 PM

[mostyfriedman]

I can do it in one line of scheme or common lisp