Split list python by index

How do I split a list into sub-lists based on index ranges?

e.g. original list:

list1 = [x,y,z,a,b,c,d,e,f,g]

using index ranges 0–4:

list1a = [x,y,z,a,b]

using index ranges 5–9:

list1b = [c,d,e,f,g]

I already known the [variable] indices of list elements which contain certain string and want to split the list based on these index values.

Also need to split into variable number of sub-lists, i.e.:

list1a
list1b
.
.
list1[x]

mkrieger1

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asked Sep 2, 2013 at 10:15

1

In python, it's called slicing. Here is an example of python's slice notation:

>>> list1 = ['a','b','c','d','e','f','g','h', 'i', 'j', 'k', 'l']
>>> print list1[:5]
['a', 'b', 'c', 'd', 'e']
>>> print list1[-7:]
['f', 'g', 'h', 'i', 'j', 'k', 'l']

Note how you can slice either positively or negatively. When you use a negative number, it means we slice from right to left.

answered Sep 2, 2013 at 10:20

TerryATerryA

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1

Note that you can use a variable in a slice:

l = ['a',' b',' c',' d',' e']
c_index = l.index["c"]
l2 = l[:c_index]

This would put the first two entries of l in l2

answered Sep 2, 2013 at 10:33

0

If you already know the indices:

list1 = ['x','y','z','a','b','c','d','e','f','g']
indices = [[0, 4], [5, 9]]
print [list1[s:e+1] for s,e in indices]

Note that we're adding +1 to the end to make the range inclusive...

answered Sep 2, 2013 at 10:31

Jon Clements♦Jon Clements

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list1a=list[:5]
list1b=list[5:]

answered Sep 2, 2013 at 10:17

no1no1

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5

One of the ways to do it if you have multiple indexes or know the range of indexes you need to get:

split_points - points where you will split your string or list

k - the range you need to split, example = 3

split_points = [i for i in range[0, len[string], k]]

parts = [string[ind:ind + k] for ind in split_points]

answered Apr 11, 2021 at 18:32

list1=['x','y','z','a','b','c','d','e','f','g']
find=raw_input["Enter string to be found"]
l=list1.index[find]
list1a=[:l]
list1b=[l:]

answered Sep 2, 2013 at 10:28

no1no1

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0

Consider the core pesudocode of the following example:

def slice_it[list_2be_sliced, indices]:
    """Slices a list at specific indices into constituent lists.
    """
    indices.append[len[list_2be_sliced]]
    return [list_2be_sliced[indices[i]:indices[i+1]] for i in range[len[indices]-1]]

answered Mar 4, 2021 at 21:17

ShadyShady

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This is the way I do it, if the input is a list of indices on which to split an array:

#input
list1 = ['x','y','z','a','b','c','d','e','f','g']
split_points = [2,5,8] 

#split array on indices:
s = split_points+[len[list1]]  #must contain index beyond last element, alternatively use directly split_points.append[len[list1]]
print[[list1[i1:i2] for i1,i2 in zip[[0]+s[:-1],s]]]

>>> [['x', 'y'], ['z', 'a', 'b'], ['c', 'd', 'e'], ['f', 'g']]

answered Jun 27 at 16:37

VincenzoooVincenzooo

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