Is there a head and tail method for Numpy array?
PythonNumpyPython Problem Overview
I loaded a csv file into 'dataset' and tried to execute dataset.head(), but it reports an error. How to check the head or tail of a numpy array? without specifying specific lines?
Python Solutions
Solution 1 - Python
For a head-like function you can just slice the array using dataset[:10].
For a tail-like function you can just slice the array using dataset[-10:].
Solution 2 - Python
You can do this for any python iterable.
PEP-3132 which is in python 3.x (https://www.python.org/dev/peps/pep-3132/) can use the * symbol for the 'rest' of the iterable.
To do what you want:
>>> import numpy as np
>>> np.array((1,2,3))
array([1, 2, 3])
>>> head, *tail = np.array((1,2,3))
>>> head
1
>>> tail
[2, 3]
Solution 3 - Python
This works well:
def nparray_tail(x: np.array, n:int):
"""
Returns tail N elements of array.
:param x: Numpy array.
:param n: N elements to return on end.
:return: Last N elements of array.
"""
if n == 0:
return x[0:0] # Corner case: x[-0:] will return the entire array but tail(0) should return an empty array.
else:
return x[-n:] # Normal case: last N elements of array.
Discussion
As a bonus, this fixes a non-intuitive corner case in the answer from @feedMe: dataset[-0:] returns the entire array, not an empty array as one would expect when requesting the last 0 elements on the tail end of the array. This is consistent with the .tail() function in Pandas.