如何在python中使用numpy在索引处添加元素

Question

I am new to python, Here I have an numpy array . Now, In this ,

I am trying to add an element in the index in the array .

for x in index:
    output_result[x:x] = [300]

But it is not getting added, index is the position. where I want to add that element. So, can any one help mw eith this ?

Answer 1

are you maybe looking for something like this:

import numpy as np

a = np.zeros(10)  # create numpy array with ten zeros
a = np.where(a == 0, 300, a)  # substitute 300 where there are zeros in array - **i assume this is what you need**

print(a)  # print generated array
print(type(a))  # print data type to show a numpy array was generated

or do you want to "append" a new element?

Answer 2

With a Python list, you can insert a value with:

In [104]: alist = [0,1,2,3]                                                     
In [105]: alist[1:1]=[300]                                                      
In [106]: alist                                                                 
Out[106]: [0, 300, 1, 2, 3]

But this does not work with ndarray . The array size is fixed. The best you can do is create a new array, with original values and the new one(s).

np.insert is a function that can do that. Since the operation is not particularly efficient, it's best to do a whole set of inserts at once, rather than do it iteratively.

In [108]: np.insert(np.arange(4),1,300)                                         
Out[108]: array([  0, 300,   1,   2,   3])
In [109]: np.insert(np.arange(4),[1,2],[300,400])                               
Out[109]: array([  0, 300,   1, 400,   2,   3])

(Even with a list, iterative insertion can be tricky, since each insertion changes the size of the list. The insertion point has to take that into account (unless you iterate from the end).)