Elegant way to REDUCE a 2D array into 1D

Given the following 2D array: var arr = [[1,2,3],[4,5,6],[7,8,9]]

How can get [1,4,7] without using for loops?

My simplest solution is transposing and returning only the first (0th) row.
There must be a more elegant solution, Perhaps something that I can chain onto an array to make it a one-liner?