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Can't understand the difference between select and collect methods. Also want to know when to use each.
Enumerable#collect (or Enumerable#map) returns a result of applying block to each items.
[1, 2, 3, 4].collect { |x| x > 2 }
# => [false, false, true, true]
While Enumerable#select returns an array of filtered items:
[1, 2, 3, 4].select { |x| x > 2 }
# => [3, 4]
Related
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I have the following array:
[1,1,3,3,3,3,1023,1023,1,3,3,3, ...]
Is there a way to sort the array in a way where the items can appear more mixed up?
Like:
[1, 3, 1023, 3, 1, 3, 1023, ...]
You could shuffle
a=[1,1,3,3,3,3,1023,1023,1,3,3,3]
p a.shuffle
Output
[1023, 1, 1, 1, 3, 3, 1023, 3, 3, 3, 3, 3]
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I'm new to rails and I was wondering how I compare the first value of array "a" if it is greater than the first value of array "b"?
Example:
a = [1, 2, 3]
b = [3, 2, 1]
How do I check if a[0] is greater than b[0].
You can use the first method:
a = [1, 2, 3]
b = [3, 2, 1]
a.first > b.first #=> false
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How can I remove elements from a given array of integers that are evenly divisible by 3? A new array should be returned and the original array should not be altered.
For example, if
array = [1,2,3,4,1,5,2,6,7,8,9,10,7,11,12,13,14,15]
the array
[1, 2, 4, 1, 5, 2, 7, 8, 10, 7, 11, 13, 14]
should be returned.
Just found it:
array.reject{|a| a % 3 == 0}
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I had 10 items in total. I lost all of them in 3 days: 5 items on the 1st day, 3 items on the 2nd day, and 2 items on the last day. I need to get an array [5, 2, 0] of remaining items at the end of each day. How can I get the array, given total 10 and the array of lost items [5, 3, 2]?
[5, 3, 2].each_with_object([10]){|e, a| a.push(a.last - e)}.drop(1)
# => [5, 2, 0]
Know why you need the complication drop(1)? It is because, without it, the answer makes more logical sense. Your requirement is what was complicated.
[5, 3, 2].each_with_object([10]){|e, a| a.push(a.last - e)}
# => [10, 5, 2, 0]
The initial 10 represents the initial state.
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I currently have this code
def objects(ids)
array = []
ids.each do |id|
array << object(id) # => #<object[id]>
end
array
end
objects([1, 2, 3])
# => [#<object1>, #<object2>, #<object3>]
It seems like there should be a cleaner way to do this. Can anyone help?
EDIT
This is what works
[1, 2, 3].map do |id|
object(id)
end
ORIGINAL
go this way:
[1, 2, 3].map(&:object_id)
# => [3, 5, 7]
def objects(ids)
ids.map(&:object_id)
end
objects([1, 2, 3])
# => [3, 5, 7]