CODEWITHSUNDEEP
python
begin.py
begin.py

Reputation: 161

Selective iteration over list

I have a huge list which looks as follows:

[ '0', '21', '51', '67', '96', '102', '128', '130', '0', '11', '36', '53', '81', '86', '113', 116', '0', '21', '48', '64', '91', '95','125', '139', '166', '175', '200', '205']

I have to carry out simple subtraction over the elements of the list such that:

//Consider 2 variables a & b//

a should store the difference between 0-21 (it should be 21-0 to avoid negative values)

then

b should store the difference between 21-51 (it should be 51-21 to avoid negative values)

then again

a should store the difference between 51-67 (it should be 67-51 to avoid negative values)

and then

b = 67-96
a = 96-102
b = 102-128
a = 128-130

There should be no subtraction between 130 and the following 0. The new iteration should begin from 0-11,11-36 and so on till the next 0 is encountered.

I am completely out of ideas as to how do i proceed with this step.

Upvotes: 1

Views: 323

Answers (3)

user1922460
user1922460

Reputation:

As long as the list contains an even number of elements this will work:

# original list
l = ['0', '21', '51', '67', '96', '102', '128', '130']

# convert items in list to integers
l = map(lambda x: int(x), l)

# split the list in two, even indices in p, odd indices in q
p = l[::2]
q = l[1::2]

# print out the calculations
for n in range(len(p)):
    print 'abs(%s - %s) = %s' % (p[n], q[n], abs(p[n]-q[n]))

It prints out like so:

abs(0 - 21) = 21
abs(51 - 67) = 16
abs(96 - 102) = 6
abs(128 - 130) = 2

If you are unaware of what slice copies do in the above code, check this out:

>>> l[::2]
['0', '51', '96', '128']
>>> l[1::2]
['21', '67', '102', '130']

The syntax is like so list_name[starting_point:ending_point:increment_by].

Upvotes: 1

Necrolyte2
Necrolyte2

Reputation: 748

li = [ 0, '21', '51', '67', '96', '102', '128', '130', '0', '11', '36', '53', '81', '86', '113', '116', '0', '21', '48', '64', '91', '95','125', '139', '166', '175', '200', 205]


li = [(int(li[i]),int(li[i+1])) for i in range( len( li ) - 1 ) if li[i+1] != '0']


for a, b in li:
    x = abs(a - b)
    print '|%3d - %3d| = %3d' % (a,b,x)

Upvotes: 0

Hai Vu
Hai Vu

Reputation: 40773

Your description of the problem is still unclear, from what I understand, this might be what you are looking for:

li = [ 0, '21', '51', '67', '96', '102', '128', '130', '0', '11', '36', '53', '81', '86', '113', '116', '0', '21', '48', '64', '91', '95','125', '139', '166', '175', '200', 205]   

# Convert all items to integers for calculations
li = [int(x) for x in li]

for x, y in zip(li, li[1:]):
    if y != 0:
        a = abs(x - y)      
        print '|%3d - %3d| = %3d' % (x, y, a)
    else:
        print ''

Output:

|  0 -  21| =  21
| 21 -  51| =  30
| 51 -  67| =  16
| 67 -  96| =  29
| 96 - 102| =   6
|102 - 128| =  26
|128 - 130| =   2

|  0 -  11| =  11
| 11 -  36| =  25
| 36 -  53| =  17
| 53 -  81| =  28
| 81 -  86| =   5
| 86 - 113| =  27
|113 - 116| =   3

|  0 -  21| =  21
| 21 -  48| =  27
| 48 -  64| =  16
| 64 -  91| =  27
| 91 -  95| =   4
| 95 - 125| =  30
|125 - 139| =  14
|139 - 166| =  27
|166 - 175| =   9
|175 - 200| =  25
|200 - 205| =   5

Upvotes: 1

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