list index out of range when iterating through a 2d array

Question

As you can see, the following array called routine has a series of other arrays inside of it.

[['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips'], [], [], [], ['Tricep Kickbacks', 'Overhead Dumbell Extensions'], [], []]

I have tried to copy each item inside this array into a new array. However when i did so i got this output and the following error message.

Bench Press
Inner Chest Push
Smith Machine Bench Press
Cable Crossover
IndexError: list index out of range

Clearly the code works through the first array inside the 2d array, however stops after that.

This is the code used to generate the above error message.

newarray=[]
for x in range(len(routine)-1):
    for i in range(len(routine)-1):
        temp = routine[x][i]
        print (temp)
        newarray.append(temp)

Is there a way in which i can join up these arrays so that there is only one array that looks like this.

['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips','Tricep Kickbacks', 'Overhead Dumbell Extensions']

Think about len() for a second. It does not recurse into the elements, it just returns the length of the outer list. And yet you are using it for both your outer and inner loop. — Mad Wombat, Jan 04 '19 at 21:24
see also: https://stackoverflow.com/questions/952914/how-to-make-a-flat-list-out-of-list-of-lists — Steven Graham, Jan 04 '19 at 21:30

hqkhan · Answer 1 · 2019-01-04T21:32:13.173

If you have nested lists you can try using list comprehension:

routine = [['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips'], [], [], [], ['Tricep Kickbacks', 'Overhead Dumbell Extensions'], [], []]
new_routine = [machine for machines in routine for machine in machines]
print(new_routine)
# ['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips', 'Tricep Kickbacks', 'Overhead Dumbell Extensions']

This only works if you have list of lists or two levels deep.

To change your code, we can do the following to obtain the same result:

newarray = []
for x in range(len(routine)):
    for i in range(len(routine[x])):
        newarray.append(routine[x][i])

print(newarray)
#['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips', 'Tricep Kickbacks', 'Overhead Dumbell Extensions']

Notice that I removed the -1 from your code. range(start, end) goes from start to end-1aka the entire array since arrays start from 0. That said, you don't need the -1.

score 0 · Answer 2 · answered Jan 04 '19 at 21:28

0

You can try this :

for e in routine:
    new_list += e

answered Jan 04 '19 at 21:28

John Doe

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score 0 · Answer 3 · answered Jan 04 '19 at 21:29

This is what you want:

routine = [['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips'], [], [], [], ['Tricep Kickbacks', 'Overhead Dumbell Extensions'], [], []]


newarray=[]
for i in routine:
        for ii in i:
                newarray.append(ii)

print(newarray) #Output: ['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips', 'Tricep Kickbacks', 'Overhead Dumbell Extensions']

score 0 · Answer 4 · answered Jan 04 '19 at 21:29

0

You don't need to use index. python can do it as simple as :

newlist=[]
for alist in routine:
    for element in alist:
        newlist.append(element)

answered Jan 04 '19 at 21:29

B. M.

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score 0 · Answer 5 · answered Jan 04 '19 at 21:31

using chain

from itertools import chain
a=[['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips'], [], [], [], ['Tricep Kickbacks', 'Overhead Dumbell Extensions'], [], []]
list(chain(*a))

Output

['Dumbell Press',
 'Chest Press Machine',
 'Smith Machine Bench Press',
 'Angled Dips',
 'Tricep Kickbacks',
 'Overhead Dumbell Extensions']

score 0 · Answer 6 · answered Jan 04 '19 at 21:32

For nested lists, a robust solution to combine all components into a single list can be done using chain.from_iterable

oldlist = [['Dumbell Press', 'Chest Press Machine', 'Smith Machine Bench Press', 'Angled Dips'], [], [], [], ['Tricep Kickbacks', 'Overhead Dumbell Extensions'], [], []]
from itertools import chain
result = list(chain.from_iterable(oldlist))
print(result)
#Output:
['Dumbell Press',
 'Chest Press Machine',
 'Smith Machine Bench Press',
 'Angled Dips',
 'Tricep Kickbacks',
 'Overhead Dumbell Extensions']

list index out of range when iterating through a 2d array

6 Answers6