I have an a array of values
a = np.array([0,3,4,5,12,3,78,53,52])
I would like to move the last three elements in the array starting from the index 3 in order to have
a
array([ 0, 3, 4, 78, 53, 52, 5, 12, 3])
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4 Answers
You can use slicing and concatenation.
np.concatenate((a[:3], a[-3:], a[3:-3]))
1 Comment
fountainhead
We just need to perform three number-swap operations. Your solution will will involve making copies of all the other (bigger) chunks of data too. Needless, don't you think?
Try this using np.delete() and np.insert():
a = np.array([0,3,4,5,12,3,78,53,52])
index = 6
another_index = 0
v = a[index]
np.delete(a,index)
np.insert(a, another_index, v)
Comments
This is just a number-swapping problem -- not a numpy problem.
Any solution to this problem that involves numpy functions such as concatenate, delete, insert, or even slicing, is inefficient, involving unnecessary copying of data.
This should work, with minimum copying of data:
a[3],a[4],a[5], a[-3],a[-2],a[-1] = a[-3],a[-2],a[-1], a[3],a[4],a[5]
print(a)
Output:
[ 0 3 4 78 53 52 5 12 3]
Comments
Starting with
a = np.array([0,3,4,5,12,3,78,53,52])
You can just do:
newa=[]
for index, each in enumerate(a):
if index<3:
newa.append(a[index])
else:
newa.append(a[3+index%6])
giving the resulting newa to be:
[0, 3, 4, 78, 53, 52, 5, 12, 3]
