`numpy:digitize`

source: /numpy/lib/_function_base_impl.py :5651

Signature

def digitize ( x , bins , right = False )

Summary

Return the indices of the bins to which each value in input array belongs.

Extended Summary

=========  =============  ============================
`right`    order of bins  returned index `i` satisfies
=========  =============  ============================
``False``  increasing     ``bins[i-1] <= x < bins[i]``
``True``   increasing     ``bins[i-1] < x <= bins[i]``
``False``  decreasing     ``bins[i-1] > x >= bins[i]``
``True``   decreasing     ``bins[i-1] >= x > bins[i]``
=========  =============  ============================

If values in x are beyond the bounds of bins, 0 or len(bins) is returned as appropriate.

Parameters

x : array_like: Input array to be binned. Prior to NumPy 1.10.0, this array had to be 1-dimensional, but can now have any shape.
bins : array_like: Array of bins. It has to be 1-dimensional and monotonic.
right : bool, optional: Indicating whether the intervals include the right or the left bin edge. Default behavior is (right==False) indicating that the interval does not include the right edge. The left bin end is open in this case, i.e., bins[i-1] <= x < bins[i] is the default behavior for monotonically increasing bins.

Returns

indices : ndarray of ints: Output array of indices, of same shape as x.

Raises

: ValueError: If bins is not monotonic.
: TypeError: If the type of the input is complex.

Notes

If values in x are such that they fall outside the bin range, attempting to index bins with the indices that digitize returns will result in an IndexError.

numpy.digitize is implemented in terms of numpy.searchsorted. This means that a binary search is used to bin the values, which scales much better for larger number of bins than the previous linear search. It also removes the requirement for the input array to be 1-dimensional.

For monotonically increasing bins, the following are equivalent

np.digitize(x, bins, right=True)
np.searchsorted(bins, x, side='left')

Note that as the order of the arguments are reversed, the side must be too. The searchsorted call is marginally faster, as it does not do any monotonicity checks. Perhaps more importantly, it supports all dtypes.

Examples

import numpy as np
x = np.array([0.2, 6.4, 3.0, 1.6])
bins = np.array([0.0, 1.0, 2.5, 4.0, 10.0])
inds = np.digitize(x, bins)
inds
for n in range(x.size):
  print(bins[inds[n]-1], "<=", x[n], "<", bins[inds[n]])

✓

x = np.array([1.2, 10.0, 12.4, 15.5, 20.])
bins = np.array([0, 5, 10, 15, 20])
np.digitize(x,bins,right=True)
np.digitize(x,bins,right=False)

✓

Aliases

numpy.digitize