how to apply a mask from one array to another array?

I had a similar issue, but involving loads more masking commands and more arrays to apply them. My solution is that I do all the masking on one array and then use the finally masked array as the condition in the mask_where command.

For example:

y = np.array([2,1,5,2])                         # y axis
x = np.array([1,2,3,4])                         # x axis
m = np.ma.masked_where(y>5, y)                  # filter out values larger than 5
new_x = np.ma.masked_where(np.ma.getmask(m), x) # applies the mask of m on x

The nice thing is you can now apply this mask to many more arrays without going through the masking process for each of them.