[Numpy-discussion] Quick array value assignment based on common values

[PHobson at Geosyntec.com]

Hey folks,

I've one array, x, that you could define as follows:
[[1, 2.25],
 [2, 2.50],
 [3, 2.25],
 [4, 0.00],
 [8, 0.00],
 [9, 2.75]]

Then my second array, y, is:
[[1, 0.00],
 [2, 0.00],
 [3, 0.00],
 [4, 0.00],
 [5, 0.00],
 [6, 0.00],
 [7, 0.00],
 [8, 0.00],
 [9, 0.00],
 [10,0.00]]

Is there a concise, Numpythonic way to copy the values of x[:,1] over to y[:,1] where x[:,0] = y[:,0]? Resulting in, z:
[[1, 2.25],
 [2, 2.50],
 [3, 2.25],
 [4, 0.00],
 [5, 0.00],
 [6, 0.00],
 [7, 0.00],
 [8, 0.00],
 [9, 2.75],
 [10,0.00]]

My current task has len(x) = 25000 and len(y) = 350000 and looping through is quite slow unfortunately.

Many thanks,
-paul