summing together elements in list in python

Question

I have two lists, t and e, of the same size: to each element t[i] corresponds an element e[i]. I want to print each pair t[i] e[i], but summing together elements e[i] and e[i-1] whenever the corresponding t[i] and t[i-1] are closer than 1. In this case, elements e[5] and e[4] should be summed up, since the corresponding t[5]-t[4]<1. The point is, I want to REPLACE the 4th elements with the 4th+5th elements, without printing the 5th elements. My code is:

t = [1, 5, 10, 16, 20, 21, 28, 33, 39, 42, 45, 50, 56]
e = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M']

for j in range(1,12):
    if t[j]-t[j-1] <= 1:
        print t[j-1], e[j-1]+e[j]
    else:
        if t[j] > t[j-1]:
            print t[j-1], e[j-1]

But this gives me:

1 A
5 B
10 C
16 D
20 EF
21 F
28 G
33 H
39 I
42 J
45 K

I don't want to print 21 F, as it is already summed in the 20 EF. How can I do that? Is there a way to increase the counter i at the end of the if condition? Thank you in advance.

Related built-in functions: [`len()`](https://docs.python.org/3/library/functions.html#len), [`zip()`](https://docs.python.org/3/library/functions.html#zip) and [`enumerate()`](https://docs.python.org/3/library/functions.html#enumerate). — handle, May 10 '17 at 07:30

papey · Answer 1 · 2017-05-10T08:14:26.267

1

Another solution is a while loop :

t = [1, 5, 10, 16, 20, 21, 28, 33, 39, 42, 45, 50, 56]
e = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M']

j = 1
while j < len(t):
    if t[j]-t[j-1] <= 1:
        print t[j-1], e[j-1]+e[j]
        j += 1
    else:
        if t[j] > t[j-1]:
            print t[j-1], e[j-1]
    j += 1

edited May 10 '17 at 08:14

answered May 10 '17 at 07:31

papey

3,854
1
19
18

Thanks, I didn't think about the while loop! I was trying to increase the counter from inside the for loop and it didn't work! – urgeo May 10 '17 at 07:41
Ok, yeah, that's maybe the best solution. ^^ – Daniel Frühauf May 10 '17 at 07:46
1

Produces wrong result. First line of output is `"56 MA"`. Thats because you access `t[-1]`, which is 56, in the first iteration. – timgeb May 10 '17 at 08:00

score 0 · Answer 2 · answered May 10 '17 at 08:28

If it's just about the output:

for i in range(0, len(t)):
    if i<1:
        print( t[i], e[i], end="")
    else:
        if t[i] - t[i-1] > 1:
            print()
            print( t[i], e[i], end="")
        else:
            print( e[i], end="")

prints

1 A
5 B
10 C
16 D
20 EF
28 G
33 H
39 I
42 J
45 K
50 L
56 M

score -1 · Answer 3 · edited May 23 '17 at 12:26

-1

Either you use the solution down here or you look at this post: Skip over a value in the range function in python

t = [1, 5, 10, 16, 20, 21, 28, 33, 39, 42, 45, 50, 56]
e = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M']

skip = False
for j in range(len(t)):
    if not skip:
        if t[j]-t[j-1] <= 1:
            print t[j-1], e[j-1]+e[j]
            skip = True
        else:
            if t[j] > t[j-1]:
                print t[j-1], e[j-1]
    else:
        skip = False

>1 A
>5 B
>10 C
>16 D
>20 EF
>28 G
>33 H
>39 I
>42 J
>45 K
>50 L

edited May 23 '17 at 12:26

Community

1
1

answered May 10 '17 at 07:27

Daniel Frühauf

311
1
2
12

What about `"56 M"`? – timgeb May 10 '17 at 08:03
Just copied the code from OP. The static range instead of len(t) or something similar is another chapter. – Daniel Frühauf May 10 '17 at 08:12

summing together elements in list in python

3 Answers3