Ruby transforming a hash, combining multiple values

Question

Consider I have an array of hashes (which is my map/reduced output from MongoDB) which look similar to the following:

[ 
  {"minute"=>30.0, "hour"=>15.0, "date"=>5.0, "month"=>9.0, "year"=>2011.0, "type"=>10.0, "count"=>299.0},
  {"minute"=>0.0, "hour"=>16.0, "date"=>5.0, "month"=>9.0, "year"=>2011.0, "type"=>10.0, "count"=>477.0},
  ...
]

But I don't want all of those time related keys and values, I'd like to combine them into a date object for each object, also would it not be more efficient to be using symbols as my keys rather than strings?

[
  {timestamp: DateTime.new(2011.0, 9.0, 5.0, 15.0, 30.0), count: 299, type: 10},
  {timestamp: DateTime.new(2011.0, 9.0, 5.0, 16.0, 0.0), count: 477, type: 10},
  ...
]

Any help on this would be really awesome. Thanks!

it's just a map, I don't see the problem... show at least what you've tried. — tokland
– tokland, Commented Oct 6, 2011 at 7:52

mu is too short · Accepted Answer · 2011-10-06 08:03:34Z

2

The straight forward way is probably as good as you're going to get, if you're array is a then:

pancakes = a.map do |h|
    {
        :timestamp => DateTime.new(h['year'], h['month'], h['date'], h['hour'], h['minute']),
        :count     => h['count'].to_i,
        :type      => h['type'].to_i
    }
end

edited Oct 6, 2011 at 8:03

answered Oct 6, 2011 at 7:53

mu is too short

436k71 gold badges863 silver badges822 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

tokland Over a year ago

+1, but why destroy "a"? b = a.map ... Also, it may look better this way: DateTime.new(*h.values_at('year', 'month', 'date', 'hour', 'minute'))

mu is too short Over a year ago

@tokland: How about pancakes instead of b? I got the impression that he wanted to replace it. I'd probably go with values_at if I had the keys in an array (and then we'd have a double splat!) or if I needed a longer variable name than h but it doesn't make that much difference here.

tokland Over a year ago

I would have gone for "cupcakes", but "pancakes" is also good ;-) I think that following FP principles -even if you pay a bit of memory/cpu penalty in a language like Ruby- is worth it. I think it's good pedagogy to mention it, some programmers haven't heard about FP and keep updating variables inplace for no good reason.

mu is too short Over a year ago

@tokland: I'm a Fargo fan so it is always pancakes. I'm not one to complain about reasonable criticism.

Collectives™ on Stack Overflow

Ruby transforming a hash, combining multiple values

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related