Get index of array starting from last element

Question

How is that i get the reverse iteration using the following code. Should I be using the reduce function or something?

Example:

for i in range(4):
    print i ////0 1 2 3

how do i print the same in the reverse order

3 2 1 0

a=[5,2,1,4,3]

I also want to print the above array in reverse using the index and not a[::-1] i.e,i want to first print

 a[4] //get index starting from last how to achieve this
 a[3]
 a[2]
 a[1]
 a[0]

range(4, 0, -1) creates a reverse range. Don't understand second part of your quetion, though. — kirilloid
– kirilloid, Commented Feb 20, 2012 at 9:57
Yes, it should be range(3, -1, -1) and solution with reversed is better — kirilloid
– kirilloid, Commented Feb 20, 2012 at 10:04
For the last part of your question, maybe for i, x in reversed(list(enumerate(a))) will suit better than for i in range(len(a), -1, -1)? — Lauritz V. Thaulow
– Lauritz V. Thaulow, Commented Feb 20, 2012 at 10:10

eumiro · Accepted Answer · 2012-02-20 09:56:41Z

5

Use the reversed function:

for i in reversed(range(4)):
    print i

prints:

and

a=[5,2,1,4,3]
for i in reversed(a):
    print i

prints

answered Feb 20, 2012 at 9:56

eumiro

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Comments

Zain Khan · Accepted Answer · 2012-02-20 09:57:07Z

1

One approach involves reversing a list before iterating over it. Though this technique wastes computer cycles, memory, and lines of code:

rseqn = list(seqn)
rseqn.reverse()
for value in rseqn:
    print value

answered Feb 20, 2012 at 9:57

Zain Khan

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Comments

user647772 · Accepted Answer · 2012-02-20 09:59:14Z

0

This works:

range(4, -1, -1)
// [4, 3, 2, 1, 0]

answered Feb 20, 2012 at 9:59

user647772

Comments

Nishant · Accepted Answer · 2012-02-20 09:59:39Z

0

>>> for i in reversed(range(4)):
...   print(i)
...
3
2
1
0

answered Feb 20, 2012 at 9:59

Nishant

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Comments

Ade YU · Accepted Answer · 2012-02-20 10:00:02Z

0

len() returns the length of a list. So you can use len(a)-1 to get the last index of list a .

answered Feb 20, 2012 at 10:00

Ade YU

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Comments

Michel Keijzers · Accepted Answer · 2012-02-20 10:01:49Z

0

You can use the reverse function of a list.

>>> a = [1,2,3,4]
>>> a.reverse()
>>> a
[4, 3, 2, 1]

Use the answer of eumiro for a one time reverse (i.e. if you only need it once). Otherwise use my approach because the conversion is done on the list itself.

edited Feb 20, 2012 at 10:01

answered Feb 20, 2012 at 9:55

Michel Keijzers

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