Python - 根据索引更改列表中的多个元素

Question

I'm new to python.. My question: I have a list rt, and a list with indices rtInd, which varies in size and content.

For all the indices in rtInd, I want to change the corresponding elements in rt.

Example: rt = [10,20,30,40]; rtInd = [2,3] rt = [10,20,30,40]; rtInd = [2,3]

What I want:

rt[2] = 30 + x

rt[3] = 40 + x

Can someone help me?

Thanks in advance!

Amy

Answer 1

If you have a list of indices, and you have x , you can loop through and update the values at the corresponding indices:

rt = [10,20,30,40]
rtInd = [2,3]
x = 10

for i in rtInd:
    rt[i] += x

# result:
# rt = [10, 20, 40, 50]

Answer 2

If rt is a numpy array, you could index with the list (or numpy.array ) of indices itself (must not be a tuple , to be clear, due to tuple s being used for multidimensional access, not a set of indices to modify):

# Setup
rt = numpy.array([10, 20, 30, 40], dtype=np.int64)
rtInd = [2, 3]  # Or numpy.array([2, 3])
x = 123  # Arbitrary value picked

# Actual work
rt[rtInd] += x

and that will push the work to a single operation inside numpy (potentially improving performance).

That said, numpy is a pretty heavyweight dependency; if you're not already relying on numpy , I'd stick to the simple loop described in MZ's answer .