How to remove all elements that satisfy a condition in array in Ruby?

How can I implement this in Ruby? Is there any one line of code technique? Let's say I want to get rid of all the elements which are less than 3 of an integer array.

You can use either new_array = array.reject {|x| x < 3} (reject returns a new array) or array.reject! {|x| x < 3} (reject! aka delete_if modifies the array in place).

There's also the (somewhat more common) select method, which acts like reject except that you specify the condition to keep elements, not to reject them (i.e. to get rid of the elements less than 3, you'd use new_array = array.select {|x| x >= 3}).

Probably worth pointing out that

array.reject! {|x| x < 3}

and

array.delete_if {|x| x < 3}

Are the same, but

array.reject {|x| x < 3}

Will still return the same result, but not change the "array".

  a = [ "a", "b", "c" ]
  a.delete_if {|x| x >= "b" }   #=> ["a"]