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I've been racking my brains around this for some time.
When using reduce - why is the first element returned without executing the operation defined in the block? Or am I missing a crucial point in how reduce works?
In the following example:
arr = [1, 3, 5]
arr.reduce {|sum, n| sum + (n * 3) }
#=> 25
I would have expected the result to be 27.
Since:
0 + (1 * 3) = 3
3 + (3 * 3) = 12
12 + (5 * 3) = 27
After some time playing around with it I figured out that in the first "tick" - the object from the array just get's added to the sum instead of being multiplied. So that the calculation is more like:
??? = 1
1 + (3 * 3) = 10
10 + (5 * 3) = 25
Could someone help me figure out where I've gotten off the path?
759
In Ruby, the reducer is a method called reduce . A popular requirement is to reduce a list of numbers into a single value by adding them together (aka. performing a sum operation). You can pass the reduce method a starting value (i.e. 0 in the example below), and a block.
Inject applies the block result + element. to each item in the array. For the next item ("element"), the value returned from the block is "result". The way you've called it (with a parameter), "result" starts with the value of that parameter. So the effect is adding the elements up.
Array#select() : select() is a Array class method which returns a new array containing all elements of array for which the given block returns a true value. Return: A new array containing all elements of array for which the given block returns a true value.
inject(:+) is not Symbol#to_proc, :+ has no special meaning in the ruby language - it's just a symbol.
It's in the docs.
If you do not explicitly specify an initial value for memo, then the first element of collection is used as the initial value of memo.
113
I had a similar issue with the default values in Ruby inject/reduce methods, so I've tried to visualize it:
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