Using Python's list index() method on a list of tuples or objects?

Question

Python\'s list type has an index() method that takes one parameter and returns the index of the first item in the list matching the parameter. For instance:

Answer 1

Those list comprehensions are messy after a while.

I like this Pythonic approach:

from operator import itemgetter

def collect(l, index):
   return map(itemgetter(index), l)

# And now you can write this:
collect(tuple_list,0).index("cherry")   # = 1
collect(tuple_list,1).index("3")        # = 2

If you need your code to be all super performant:

# Stops iterating through the list as soon as it finds the value
def getIndexOfTuple(l, index, value):
    for pos,t in enumerate(l):
        if t[index] == value:
            return pos

    # Matches behavior of list.index
    raise ValueError("list.index(x): x not in list")

getIndexOfTuple(tuple_list, 0, "cherry")   # = 1

Answer 2

Inspired by this question, I found this quite elegant:

>>> tuple_list = [("pineapple", 5), ("cherry", 7), ("kumquat", 3), ("plum", 11)]
>>> next(i for i, t in enumerate(tuple_list) if t[1] == 7)
1
>>> next(i for i, t in enumerate(tuple_list) if t[0] == "kumquat")
2

Answer 3

z = list(zip(*tuple_list))
z[1][z[0].index('persimon')]

Answer 4

You can do this with a list comprehension and index()

tuple_list = [("pineapple", 5), ("cherry", 7), ("kumquat", 3), ("plum", 11)]
[x[0] for x in tuple_list].index("kumquat")
2
[x[1] for x in tuple_list].index(7)
1

Answer 5

No body suggest lambdas?

Y try this and works. I come to this post searching answer. I don't found that I like, but I feel a insingth :P

    l #[['rana', 1, 1], ['pato', 1, 1], ['perro', 1, 1]]

    map(lambda x:x[0], l).index("pato") #1 

Edit to add examples:

   l=[['rana', 1, 1], ['pato', 2, 1], ['perro', 1, 1], ['pato', 2, 2], ['pato', 2, 2]]

extract all items by condition: filter(lambda x:x[0]=="pato", l) #[['pato', 2, 1], ['pato', 2, 2], ['pato', 2, 2]]

extract all items by condition with index:

    >>> filter(lambda x:x[1][0]=="pato", enumerate(l))
    [(1, ['pato', 2, 1]), (3, ['pato', 2, 2]), (4, ['pato', 2, 2])]
    >>> map(lambda x:x[1],_)
    [['pato', 2, 1], ['pato', 2, 2], ['pato', 2, 2]]

Note:_ variable only works in interactive interpreter y normal text file _ need explicti assign, ie _=filter(lambda x:x[1][0]=="pato", enumerate(l))

Answer 6

Python's list.index(x) returns index of the first occurrence of x in the list. So we can pass objects returned by list compression to get their index.

>>> tuple_list = [("pineapple", 5), ("cherry", 7), ("kumquat", 3), ("plum", 11)]
>>> [tuple_list.index(t) for t in tuple_list if t[1] == 7]
[1]
>>> [tuple_list.index(t) for t in tuple_list if t[0] == 'kumquat']
[2]

With the same line, we can also get the list of index in case there are multiple matched elements.

>>> tuple_list = [("pineapple", 5), ("cherry", 7), ("kumquat", 3), ("plum", 11), ("banana", 7)]
>>> [tuple_list.index(t) for t in tuple_list if t[1] == 7]
[1, 4]