Compare two string lists with each other Python

Question

I would like to compare two string lists, locate the common strings and store the common strings in a new list.

For example:

my_list1=['      4,         -40.,         -12.\n',
 '      5,         -40.,         -15.\n',
 '      6,         -40.,         -18.\n',
 '      7,         -40.,         -21.\n',
 '      8,         -40.,         -24.\n',
 '      9,         -40.,         -27.\n',
 '     14,         -30.,         -30.\n',
 '     15,         -28.,         -30.\n']

my_list2=['49',
 '50',
 '51',
 '10',
 '53',
 '54',
 '55',
 '56',
 '57',
 '58',
 '59',
 '60',
 '6162',
 '15',
 '64',
 '65',
 '66']

What I want to do is compare each of the strings of my_list2 with the beginning of the strings in my_list1.

For example my_list1 contains '15' from my_list2 in [ '15, -28., -30.\n'] so i want a new list which is going to save all the common strings

This is called getting the intersection of the lists btw. Python probably has a built-in function for this already. — Carcigenicate
– Carcigenicate, Commented Jul 4, 2017 at 11:24

Moses Koledoye · Accepted Answer · 2017-07-04 11:25:54Z

3

You can use str.startswith which can take a tuple of items as argument. Left strip each item in the first list and check if the item startswith any of the strings in the second list:

t = tuple(my_list2)
lst = [x for x in my_list1 if x.lstrip().startswith(t)]
print lst
# ['     15,         -28.,         -30.\n']

answered Jul 4, 2017 at 11:25

Moses Koledoye

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2 Comments

Ma0 Over a year ago

nice use of the startswith() there. +1. Would it be slower with any()? Like lst = [x for x in my_list1 if any(x.lstrip().startswith(y) for y in my_list2)]. It should be the same thing, right?

Moses Koledoye Over a year ago

@Ev.Kounis No it won't. A single call (albeit with a tuple of params) will be much faster than a *n call in a gen. exp. wrapped by any.

Manish Goel · Accepted Answer · 2017-07-04 11:29:13Z

0

my_list1_new = [i.strip().split(",")[0] for i in my_list1 ]
for i in my_list2:
    if i in my_list1_new:
        print(my_list1[my_list1_new.index(i)])

answered Jul 4, 2017 at 11:29

Manish Goel

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