Ruby: Flatten arrays by only one level
Array#flatten
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by default flattens an array recursively. To only flatten the array for e.g. one level, it takes an optional argument.
# Flattens the array recursively
>> [1, [2, [3]]].flatten
=> [1, 2, 3]
# Flattens the array the given number of times
>> [1, [2, [3]]].flatten(1)
=> [1, 2, [3]]
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