[](*args) public

Element Reference — Returns the element at index, or returns a subarray starting at the start index and continuing for length elements, or returns a subarray specified by range of indices.

Negative indices count backward from the end of the array (-1 is the last element). For start and range cases the starting index is just before an element. Additionally, an empty array is returned when the starting index for an element range is at the end of the array.

Returns nil if the index (or starting index) are out of range.

a = [ "a", "b", "c", "d", "e" ]
a[2] +  a[0] + a[1]    #=> "cab"
a[6]                   #=> nil
a[1, 2]                #=> [ "b", "c" ]
a[1..3]                #=> [ "b", "c", "d" ]
a[4..7]                #=> [ "e" ]
a[6..10]               #=> nil
a[-3, 3]               #=> [ "c", "d", "e" ]
# special cases
a[5]                   #=> nil
a[6, 1]                #=> nil
a[5, 1]                #=> []
a[5..10]               #=> []
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July 29, 2010
4 thanks

Getting (n..end) reloaded

You can do

August 24, 2009
1 thank

Getting (n..end)

It would seem like it would be possible to say, get everything from element i and to the end by saying

a[i, -1] # "From 2 to the last element"

but since the second parameter does not say the ending index, but instead the length, this is not possible and you will get nil from the above code.

What you should do instead is using that the length can be specified longer then how long it is going to be:

b = [1, 2, 3]
# Return up to a million elements
# (not "return an array WITH 1 million elements")
b[2, 1_000_000] #=> [3]

# Size is guaranteed to never be shorter
# than our returned value should be
a[i, a.size]

It is a waste to do something like this:

a[i, a.size - i]
August 17, 2010
1 thank

Getting n..end in Rails

Nice one, henning. For anyone using Rails (ActiveSupport) a handy method called #from is also present.

[1, 2, 3, 4, 5].from(2) # => [3, 4, 5]

So our example would be


It reads a lot better