How to duplicate list values using matching value index from another list?

Question

I have two lists:

A = [476, 1440, 3060, 3060, 500,500]
B = [0,4,10,15]

NOTE: length of list B will always be equal to individual plus number of paired values in list A. Updated list B will match the length of the list A.

I want to check for duplicate values in the list A and use its indexed position to duplicate corresponding value in the list B. For example, list A has A[2]=A[3] and A[4]=A[5] (3060 and 500), so based on this I want to duplicate B[2] and B[3] and add these at B[3] and B[5] respectively. So updated list B would look like:

B = [0,4,10,10,15,15]

I tried following to get start index of duplicate values:

C = [x==A[i-1] for i,x in enumerate(A)][1:]

for idx,l in enumerate(C):
    if l == True:
        print "idx"

But running short to incorporate this change into list B. Any suggestions would be appreciative.

List B would be unique, always? and what if the same number occurs more than twice in A — thefourtheye
– thefourtheye, Commented Jan 22, 2014 at 7:51
Both lists will continuously change. Same number will only occur twice in list A, not more than that. — Ibe
– Ibe, Commented Jan 22, 2014 at 7:52
If A = [200, 500, 3060, 3060, 500] and B = [0,4,10,15] what would be your answer? — ssm
– ssm, Commented Jan 22, 2014 at 7:55
This will not be the case. Duplicate values in A will be adjacent to each other. — Ibe
– Ibe, Commented Jan 22, 2014 at 7:59
You should add a better example, one that contains multiple repeated items. — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Jan 22, 2014 at 8:11

mshsayem · Accepted Answer · 2014-01-22 08:59:42Z

2

Here is a naive implementation (not sure if I got your requirement correct):

>>> from itertools import groupby
>>> A = [476, 1440, 3060, 3060, 500, 500]
>>> B = [0, 4, 10, 15]
>>> Result = []
>>> for i, g in enumerate(groupby(A)):
        Result += [B[i]] * len(list(g[1]))


>>> Result
[0, 4, 10, 10, 15, 15]

edited Jan 22, 2014 at 8:59

answered Jan 22, 2014 at 8:10

mshsayem

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1 Comment

Ibe Over a year ago

an additional thing: if I have more than one list to adjust, how to include them as part of the single for loop you have provided in answer?

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