Check if list element in list is in another list in list in Python

Question

Given the data below, how would I print elements of a list within a list that were present within another list within a different list?

Example;

a = [['P101','John','Jones','100'], ['P102','Steve','Woodhouse','500'], ['P103','Ben','Jacobs','60']]
b = [['P101','John','Jones','250'], ['P102','Steve','Woodhouse','500']

I would like to print 'John Jones' & 'Steve Woodhouse' even though 'John Jones''s list is slightly different (his ID 'P101' still appears in both lists). I would also like to print 'Steve Woodhouse' but not 'Ben Jacobs', because he is not present in both lists.

Bhargav Rao · Accepted Answer · 2015-02-26 16:58:01Z

1

One of the approaches can be. This checks if the same ID is present in both the lists. (Not a efficient one)

>>> for i in a:
...     if i[0] in (j[0] for j in b):
...         print("{} {}".format(i[1],i[2]))
... 
John Jones
Steve Woodhouse

answered Feb 26, 2015 at 16:58

Bhargav Rao

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2 Comments

B-B. Over a year ago

This is awesome, and works perfectly, however as you mention it is not efficient (I will be working with rather large data sets), is this the best approach to take?

Bhargav Rao Over a year ago

@B-B. Yep this is a slow way! But it will work quite well if you store (j[0] for j in b) in a variable and leave the print to some file as screen printing is a slow process :)

Scis · Accepted Answer · 2015-02-26 17:20:49Z

1

You could create dictionaries instead and then intersect the keys using the viewkeys function like so:

a = [['P101','John','Jones','100'], ['P102','Steve','Woodhouse','500'], ['P103','Ben','Jacobs','60']]
b = [['P101','John','Jones','250'], ['P102','Steve','Woodhouse','500']]

ad = { p[0]: "{} {}".format(p[1],p[2]) for p in a}
bd = { p[0]: "{} {}".format(p[1],p[2]) for p in b}
common_id = ad.viewkeys() & bd.viewkeys()

for id in common_id:
    print ad[id]

Live example

answered Feb 26, 2015 at 17:20

Scis

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