NOTE: My need isn't this e.g. List[2:4] = 5
Suppose my List=[1,2,3,4,5,6]
I want to add 5 from index 2 to 4.
So the resultant List would be like List=[1,2,8,9,10,6]
If I have 2d array List=[[1,2,3],[4,5,6]] and want to add 5 to col 1 List=[[6,2,3],[9,5,6]]then what would be the code?
One approach is
my_list = [1,2,3,4,5]
add_item = [2,3]
new_list = [x+1 if i in add_item else x for i, x in enumerate(my_list)]
print(new_list)
This can be easily done through list comprehension.
The following function takes a 2D array 2d, a position index i and a value v, and adds v to the i-th element of each array.
def add_value(2d, i, v):
return [array[:i] + [array[i]+v] + array[i+1:] for array in 2d]
So, calling the function on the list in your example:
my_list = [[1,2,3],[4,5,6]]
add_value(my_list,0,5)
Would print out the desired output:
>>> [[6, 2, 3], [9, 5, 6]]
Numpy arrays can handle such slice operations:
import numpy as np
List = np.array([1, 2, 3, 4, 5, 6])
List[2:5] += 5
print(List)
Numpy will really come in handy for you if you have many of such tasks to do in your code. However, if it's just a one time thing in your code, you can do:
List = [1, 2, 3, 4, 5, 6]
for i in range(2, 5):
List[i] += 5
print(List)
Output:
[1, 2, 8, 9, 10, 6]
EDIT
Addressing your edit, you can also use numpy arrays like so:
import numpy as np
List = np.array([[1, 2, 3], [4, 5, 6]])
List[0] += 5
print(List)
Or using a loop:
List = [[1, 2, 3], [4, 5, 6]]
for i in range(len(List[0])):
List[0][i] += 5
print(List)
Output:
[[6, 7, 8], [4, 5, 6]]
One solution uses NumPy but my implementation is on an in-built list and other solutions are copying unnecessary elements.
So here I found the manual way to do it.
List = [[1,2,3,4,5],[6,7,8,9,10]]
# for horizontal update
colToUpdate = 2
for r in range(0,2):
A[r][colToUpdate] += add
# for vertical update
rowToUpdate = 1
for c in range(2,5):
A[rowToUpdate][c] += add
my_list = [n + 5 if i in range(2, 5) else n for i, n in enumerate(my_list)]range(2, 4):)rangeworks. :) OP wants to add to every item in indices 2 to 4 inclusive.