What's wrong with the code below?
arr=numpy.empty((2,2))
arr[0:,0:]=1
print(arr[1:,1:])
arr=([ [1, 2, 3], [ 4, 5, 6], [ 7, 8, 9] ])
print(arr[1:2, 1])
I am getting the following error and not able to slice the array( fifth line). Please help me with this.
TypeError: list indices must be integers, not tuple.
You rebind the name arr to point to a Python list in your fourth line, and so your question title doesn't quite fit: you're not slicing a 2d numpy array. lists can't be sliced the way that numpy arrays can. Compare:
>>> arr= numpy.array([ [1, 2, 3], [ 4, 5, 6], [ 7, 8, 9] ])
>>> arr
array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
>>> arr[1:2, 1]
array([5])
but
>>> arr.tolist()
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> arr.tolist()[1:2, 1]
Traceback (most recent call last):
File "<ipython-input-23-4a441cf2eaa9>", line 1, in <module>
arr.tolist()[1:2, 1]
TypeError: list indices must be integers, not tuple
arr=([ [1, 2, 3], [ 4, 5, 6], [ 7, 8, 9] ]) is a python list,not a numpy array.
You reassign arr with arr=([ [1, 2, 3], [ 4, 5, 6], [ 7, 8, 9] ]) to a list.
Make it a numpy array:
In [37]: arr = numpy.array([ [1, 2, 3], [ 4, 5, 6], [ 7, 8, 9] ])
In [38]: arr
Out[38]:
array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
In [39]: (arr[1:2, 1])
Out[39]: array([5])
