使用numpy索引的元组

Question

It drives me crazy, but I can't figure it out I have a data matrix of (10000,4)

I need to select some rows where the elements of column 0

ind1=np.where( (data[:,0]>55) & (data[:,0]<65) )

I want to keep that data only so

keep_data=data[ind1,:]

But keep_data is now (1,10000,4)

Why is that?

PS What i do is th efollwing

keep_data=np.reshape(keep_data,(keep_data.shape[1],keep_data.shape[2]))

Answer 1

numpy.where returns a tuple.

Therefore, use ind1 = np.where((data[:,0]>55) & (data[:,0]<65))[0]

Notice the [0] indexing to select the only element of the tuple.

This is noted in the docs :

numpy.where ( condition[, x, y] )

Return elements, either from x or y, depending on condition.

If only condition is given, return the tuple condition.nonzero() , the indices where condition is True .