larray.Array.diff¶

Array.diff(self, axis=-1, d=1, n=1, label='upper')[source]¶

Calculates the n-th order discrete difference along a given axis.

The first order difference is given by out[n] = a[n + 1] - a[n] along the given axis, higher order differences are calculated by using diff recursively.

Parameters:

axis : int, str, Group or Axis, optional: Axis or group along which the difference is taken. Defaults to the last axis.
d : int, optional: Periods to shift for forming difference. Defaults to 1.
n : int, optional: The number of times values are differenced. Defaults to 1.
label : {‘lower’, ‘upper’}, optional: The new labels in axis will have the labels of either the array being subtracted (‘lower’) or the array it is subtracted from (‘upper’). Defaults to ‘upper’.

Returns:

Array: The n-th order differences. The shape of the output is the same as a except for axis which is smaller by n * d.

Examples

>>> a = ndtest('sex=M,F;type=type1,type2,type3').cumsum('type')
>>> a
sex\type  type1  type2  type3
       M      0      1      3
       F      3      7     12
>>> a.diff()
sex\type  type2  type3
       M      1      2
       F      4      5
>>> a.diff(n=2)
sex\type  type3
       M      1
       F      1
>>> a.diff('sex')
sex\type  type1  type2  type3
       F      3      6      9
>>> a.diff(a.type['type2':])
sex\type  type3
       M      2
       F      5