Canuck - 8 months ago 71
Python Question

Quick numpy array extension

I wonder if there is a trick to extending a numpy array with consecutive
numbers in between each original values, up to a user controlled default length. Perhaps there is already a built-in function that turns x into y

``````x=np.array([4,8,4,10])

y=np.array([4,5,6,7,8,9,10,11,4,5,6,7,10,11,12,13])
``````

Here the length between each element that I added was three. Speed is of the essence here. I need something like this for my column data to work in creating a sparse
matrix.

Also, if I have an array such as

``````s=np.array([0,1])
``````

is there a quick way to extend each element an arbitrary amount of
times, lets say 4 for example:

``````s=np.array([0,0,0,0,1,1,1,1])
``````

``````In [241]: (x[:,None]+np.arange(4)).ravel()
Out[241]: array([ 4,  5,  6,  7,  8,  9, 10, 11,  4,  5,  6,  7, 10, 11, 12, 13])
``````

It gets trickier if adding different amounts for each sublist.

`repeat` is useful:

``````In [242]: np.repeat(np.array([0,1]),[3,4])
Out[242]: array([0, 0, 0, 1, 1, 1, 1])
``````

`tile` is another good tool.

Source (Stackoverflow)