Bilja Bilja - 1 year ago 112
Python Question

Python: how to find elements in array x which have values close to elements in array y?

Elements in arrays x and y are floats. I would like to find elements in array x which have values as close as possible to the ones in array y (for each value in array y - one element in array x). Also array x contains >10^6 elements and array y around 10^3, and this is part of a for loop so it should be done preferably fast.

I tried to avoid making it as a new for loop so I did this, but it is very slow for a big y array

x = np.array([0, 0.2, 1, 2.4, 3, 5]); y = np.array([0, 1, 2]);
diff_xy = x.reshape(1,len(x)) - y.reshape(len(y),1);
diff_xy_abs = np.fabs(diff_xy);
args_x = np.argmin(diff_xy_abs, axis = 1);
x_new = x[args_x]

I'm new to Python, so any suggestion is welcome!

Answer Source

The following gives the desired result.

x[abs((np.tile(x, (len(y), 1)).T - y).T).argmin(axis=1)]

It tiles x for each element in y (len(y)), transposes (.T) this tiled array, subtracts y, re-transposes it, takes the absolute value of differences, determines the indexes of the minimum values using argmin (over axis=1), and finally gets the values from these indexes of x.

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