Find the index of an item in a list that starts with a user defined input

Question

Given a list such as:

lst = ['abc123a:01234', 'abcde123a:01234', ['gfh123a:01234', 'abc123a:01234']]

is there a way of quickly returning the index of all the items which start with a user-defined string, such as 'abc'?

Currently I can only return perfect matches using:

print lst.index('abc123a:01234')

or by doing this in a number of steps by finding all the elements that start with 'abc' saving these to a new list and searching the original list for perfect matches against these.

If the only quick way is to use regex how could I still have the flexibility of a user being able to input what the match should be?

You have a nested list. What is your expected output, exactly? — thefourtheye, Apr 23 '14 at 10:47
I haven't tried index with a nested list but I was hoping for [0][0], [0][1] [0][2][1], is this wrong? — PaulBarr, Apr 23 '14 at 10:50
@PaulBarr Simply put, what do you say as the index of `gfh123a:01234`? — thefourtheye, Apr 23 '14 at 10:51
@PaulBarr: also, `[0]` is not an index, it is Python indexing *syntax*; you cannot use it to retrieve the original value. — Martijn Pieters, Apr 23 '14 at 10:52
What is your *use case* here? What problem are you trying to solve? Why is your input list arbitrarily nested? — Martijn Pieters, Apr 23 '14 at 10:52
So how would I retrieve the original value? Apologies if im asking basic questions! — PaulBarr, Apr 23 '14 at 10:53
I think you need to zoom out a little here; *why* do you need to find those values. What are you going to do with them once you find them? — Martijn Pieters, Apr 23 '14 at 10:55
basically this is part of a much larger problem which I am struggling to solve. This is a genetics problem, where the list above represents a tree written in newick format. I ultimately want to find all outgroups which match a certain character string — PaulBarr, Apr 23 '14 at 10:55
Do you just want to find the groups or do you *need* the indices? — Jayanth Koushik, Apr 23 '14 at 10:56
Right, so now we are getting somewhere; any reason you are not using BioPython for this? The [`Phylo` module](http://biopython.org/wiki/Phylo) supports newick trees, for example. I am not a BioPython user myself, but it looks as if you can at least traverse such trees (and thus search). — Martijn Pieters, Apr 23 '14 at 10:56
I want to find the groups but to determine which ones are outgroups I was going to look at the indices. If you refer to [link](http://stackoverflow.com/questions/23172293/use-python-to-extract-branch-lengths-from-newick-format) you can see the type of list im dealing with. I have written code that allows me to extract just the subtree of interest but Im stuck on the next step. — PaulBarr, Apr 23 '14 at 10:58
I have never heard of BioPython before (I have only been using python for the last month or so!), I appreciate that I am probably going around this in a very long winded way — PaulBarr, Apr 23 '14 at 10:59

score 2 · Accepted Answer · edited Apr 23 '14 at 11:06

2

You can accomplish that using the following script/method (which I admit is quite primitive):

lst = ['abc123a:01234', 'abcde123a:01234', ['gfh123a:01234', 'abc123a:01234']]

user_in = 'abc'

def get_ind(lst, searchterm, path=None, indices=None):
    if indices is None:
        indices = []
    if path is None:
        path = []
    for index, value in enumerate(lst):
        if isinstance(value, list):
            get_ind(value, searchterm, path + [index], indices)
        elif value.startswith(searchterm):
            indices.append(path + [index])
    return indices

new_lst = get_ind(lst, user_in)

>>> print new_lst
[[0], [1], [2, 1]]

edited Apr 23 '14 at 11:06

Martijn Pieters

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answered Apr 23 '14 at 10:49

sshashank124

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Don't use a mutable list as the default argument here; you are not even *using* the default, but the proper way to do this would be to use `indices=None` and `if indices is None: indices = []` to kickstart that list. – Martijn Pieters Apr 23 '14 at 11:00
@MartijnPieters, Please edit my code as necessary. I admit that it is still quite raw. Thank you – sshashank124 Apr 23 '14 at 11:01
Your code doesn't handle more nesting levels correctly; the parent path cannot handle more than one index. – Martijn Pieters Apr 23 '14 at 11:04
Fixed both issues, and applied a little PEP-8 styling. – Martijn Pieters Apr 23 '14 at 11:07

Find the index of an item in a list that starts with a user defined input

1 Answers1