Python: Add value to a list at predefined indexes

Question

I have a list (aList) I need to create another list of the same length as aList (checkColumn) and add 1 at the positions defined in the index list (indexList), the positions not defined in the indexList should be 0

Input:

aList = [70, 2, 4, 45, 7 , 55, 61, 45]
indexList = [0, 5, 1]

Desired Output:

checkColumn = [1,1,0,0,0,1]

I have been experimenting around with the following code, but I get the output as [1,1]

for a in len(aList):
    if a == indexList[a]:
        checkColumn = checkColumn[:a] + [1] + checkColumn[a:]
    else:
        checkColumn = checkColumn[:a] + [0] + checkColumn[a:]

I have tried with checkColumn.insert(a, 1) and I get the same result. Thanks for the help!

Can I ask why do you need this exactly? Can you describe the problem that led to this solution? — Reut Sharabani
– Reut Sharabani, Commented Sep 3, 2018 at 15:45
aList is the id of all items, of these I have already identified the indexes of the bad items and put it in indexList. Now I want to mark in another list (check) the items that are bad (1) and those good (0) — Kay
– Kay, Commented Sep 3, 2018 at 16:30
This re-describes the problem you've presented. Not how it spawned. I think there may be a simpler solution to what you're doing on a higher-level. Good luck :) — Reut Sharabani
– Reut Sharabani, Commented Sep 3, 2018 at 16:35

Pranav Hundekari · Accepted Answer · 2018-09-03 15:54:30Z

3

Would this help?

First, you initialize checkColumn with 0

checkColumn = [0] * len(aList)

Then, loop through indexList and update the checkColumn

for idx in indexList:
    checkColumn[idx] = 1

Cheers!

answered Sep 3, 2018 at 15:54

Pranav Hundekari

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Comments

DavidG · Accepted Answer · 2018-09-03 15:49:08Z

2

You could do this in one line using a list comprehension:

aList = [70, 2, 4, 45, 7 , 55, 61, 45]
indexList = [0, 5, 1]

checkColumn = [1 if a in indexList else 0 for a in range(len(aList))]
print(checkColumn)
# [1, 1, 0, 0, 0, 1, 0, 0]

answered Sep 3, 2018 at 15:49

DavidG

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1 Comment

taras Over a year ago

You can make in even shorter with int(a in indexList)

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