How can I perform element-wise multiplication for Ruby arrays?

Question

courses, credits and points are Ruby arrays with an equal size.

gpa = (([credits, courses, points].transpose.map {|x| x.reduce(:*)}).inject{|sum,x| sum + x }).round(2)

This method prompted an error message when I was trying to run it.

Error message:

in 'each': undefined method '*' for nil:NilClass (NoMethodError)

Looks good to me. (by the way, `inject` and `reduce` are synonyms, use one or the other but not both, for clarity). **The problem is in your data** — jazzytomato, Apr 26 '15 at 10:05
separate that long code into different lines so you can easily pinpoint where the error is. — jvnill, Apr 27 '15 at 03:44
@ThomasHaratyk Thanks for raising up the synonyms. Yeah you're right. Some unexpected errors within the data. — sponavitus, Apr 27 '15 at 08:23

score 1 · Accepted Answer · answered Apr 27 '15 at 00:49

1

From the error message, it seems that some of the data is nil.

Perhaps you can attempt to force the data into floats.

It's not ideal, as you might end up with silent errors, but it's worth a shot.

try:

[credits, courses, points].transpose.map {|a| a.map {|n| n.to_f} } .map { |x| x.reduce(:*) } .inject{|sum, x| sum + x} .round(2)

It works for me even with strings and weird data (although the incompatible data is simply converted to zeros, effecting the math).

answered Apr 27 '15 at 00:49

Myst

Thanks, I found the error. It actually caused by some invalid data. – sponavitus Apr 27 '15 at 08:27
@JohnsonYeap Your welcome. I'm happy you found the error. Good luck with your coding. – Myst Apr 27 '15 at 08:30

1 Answers1