scipy.ndimage.median(input, labels=None, index=None)[source]

Calculate the median of the values of an array over labeled regions.


input : array_like

Array_like of values. For each region specified by labels, the median value of input over the region is computed.

labels : array_like, optional

An array_like of integers marking different regions over which the median value of input is to be computed. labels must have the same shape as input. If labels is not specified, the median over the whole array is returned.

index : array_like, optional

A list of region labels that are taken into account for computing the medians. If index is None, the median over all elements where labels is non-zero is returned.


median : float or list of floats

List of medians of input over the regions determined by labels and whose index is in index. If index or labels are not specified, a float is returned: the median value of input if labels is None, and the median value of elements where labels is greater than zero if index is None.


The function returns a Python list and not a Numpy array, use np.array to convert the list to an array.


>>> from scipy import ndimage
>>> a = np.array([[1, 2, 0, 1],
...               [5, 3, 0, 4],
...               [0, 0, 0, 7],
...               [9, 3, 0, 0]])
>>> labels, labels_nb = ndimage.label(a)
>>> labels
array([[1, 1, 0, 2],
       [1, 1, 0, 2],
       [0, 0, 0, 2],
       [3, 3, 0, 0]])
>>> ndimage.median(a, labels=labels, index=np.arange(1, labels_nb + 1))
[2.5, 4.0, 6.0]
>>> ndimage.median(a)
>>> ndimage.median(a, labels=labels)

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