How to add a value in a nested list that corresponding to another list?

Question

I'm setting up a linear connection and I have two list:

a = [1,1,1,2,2,3,3,3,4]
b = [1,3,7,2,3,4,7,8,9]

a[i] related to b[i]

I regrouped b as c:

c = [[1, 3], [7], [2, 3], [4], [7, 8], [9]]

I tried to add the corresponding value of a in every sublist in c to get:

d = [[1, 1, 3], [1, 7], [2 ,2, 3], [3, 4], [3, 7, 8], [4, 9]]

The first value in every sublist of c that originally in b is related to a like c[0][0] = b[0], and add a[0] to c[0], c[1][0] = b[2], so add a[2] to c[1].

If sublist in c and the first value of the sublist = b[i], add a[i] to every sublist.

I got stuck for this.

• Farhood ET: Can you elaborate more on what you are trying to do? what is the relation between A and B. Why d has only three 1s but A and B have four altogether?
• wayne64001: For every sublist in c, if sublist[0] = b[i], add a[i] to sublist. Is that Okay?

Answer 1

You could build an iterator from a and take successive slices of it using itertools.islice in order to consume it according to the length of the sublists in c, but only select the first item from each slice:

from itertools import islice
a = [1,1,1,2,2,3,3,3,4]
c = [[1, 3], [7], [2, 3], [4], [7, 8], [9]]
a_ = iter(a)
[[list(islice(a_, len(j)))[0]] + [i for i in j] for j in c]

Output

[[1, 1, 3], [1, 7], [2, 2, 3], [3, 4], [3, 7, 8], [4, 9]]

Answer 2

Another method. Basic Way.

#!/bin/python
a = [1,1,1,2,2,3,3,3,4]
b = [1,3,7,2,3,4,7,8,9]
c = [[1, 3], [7], [2, 3], [4], [7, 8], [9]]
#d = [[1, 1, 3], [1, 7], [2 ,2, 3], [3, 4], [3, 7, 8], [4, 9]]
element_count=0
d=[]
for x in c:
 print (a[element_count])
 print(x)
 d.append([a[element_count]]+x)
 element_count+=len(x)