Difference between elements of N list of size n. Python

Question

Say I have N lists of size n, eg, 5 tuples of size 3:

p = [[9, 9, 9], [17, 14, 18], [14, 15, 17], [14, 15, 17], [14, 15, 15]]

How can I find the difference between indexes of the lists, for example the index 0:

17-9 = 8
14-17 = -3
14-14 = 0
14-14 = 0

then for index 1:

14-9 = 5
15-14 = 1
15-15 = 0
15-15 = 0

then index 2, 3, 4.

I need the code to be able to do this dynamically so I can change N and n at will.

Any help will be greatly appreciated.

EDIT:

I have tried this thus far:

for i in range(10):
    for j, k in product(range(i+1), repeat=2):
        if j!=k:continue
        else:
            print p[i][j]-p[i-1][j]

This code is for tuples of size 2.

These are not tuples. Tuples are in parens, like `(9, 9, 9)`. — ulidtko, Mar 20 '13 at 15:07
It would be helpful to know what you've tried and also what you're looking for in a solution (e.g. most pythonic way of doing it, fastest, easiest to read?) — Emily, Mar 20 '13 at 15:08
what the format of the data you expect ? a list of list too ? — ornoone, Mar 20 '13 at 15:09

score 2 · Accepted Answer · answered Mar 20 '13 at 15:22

Try this:

>>> for x in zip(*p):
    for i in range(len(x)-1):
        print '{0} - {1} = {2}'.format(x[i+1],x[i],x[i+1]-x[i])


17 - 9 = 8
14 - 17 = -3
14 - 14 = 0
14 - 14 = 0
14 - 9 = 5
15 - 14 = 1
15 - 15 = 0
15 - 15 = 0
18 - 9 = 9
17 - 18 = -1
17 - 17 = 0
15 - 17 = -2

score 1 · Answer 2 · answered Mar 20 '13 at 15:14

ugly as hell, not pythonic, prone to all the errors of this world, but yet working (and at least should show you a basic logic for what you need):

In [6]: for i in range(len(p[0])):
            for j in range(1,len(p)):
               print "%d - %d = %d" % (p[j][i], p[j-1][i], p[j][i]-p[j-1][i])
   ...:         
17 - 9 = 8
14 - 17 = -3
14 - 14 = 0
14 - 14 = 0
14 - 9 = 5
15 - 14 = 1
15 - 15 = 0
15 - 15 = 0
18 - 9 = 9
17 - 18 = -1
17 - 17 = 0
15 - 17 = -2

explanation

row 1: checks for the length of your sublists, based on the first element of your max list.
row 2: does the same, starting from index one (so you can do p[1]-p[0] without worrying about out of bounds problems)
row 3: prints what you want

you could start from this to tinker around

confused_at_times · Answer 3 · 2013-03-20T15:18:41.003

1

This should do it:

for xyz in zip(*p):
   for curr_idx in xrange(len(xyz)-1):
     print xyz[curr_idx+1]-xyz[curr_idx]

edited Mar 20 '13 at 15:18

answered Mar 20 '13 at 15:16

confused_at_times

539
3
13

score 1 · Answer 4 · answered Mar 20 '13 at 15:17

1

It can easily be done using numpy:

p = numpy.array([[9, 9, 9], [17, 14, 18], [14, 15, 17], [14, 15, 17], [14, 15, 15]])
numpy.diff(p.T)

answered Mar 20 '13 at 15:17

Charles Brunet

21,797
24
83
124

score 1 · Answer 5 · answered Mar 20 '13 at 15:21

try this

p = ((9, 9, 9), (17, 14, 18), (14, 15, 17), (14, 15, 17), (14, 15, 15))
index=0
for d in range(1,len(p)):
    print "p["+str(d)+"]["+str(index)+"]-p["+str(d)+"]["+str(index)+"]=",
    print p[d][index]-p[d-1][index]

output is

p[1][0]-p[1][0]= 8
p[2][0]-p[2][0]= -3
p[3][0]-p[3][0]= 0
p[4][0]-p[4][0]= 0

Difference between elements of N list of size n. Python

5 Answers5