Geek Answers Handbook

How to find the location of an item in a list of Python lists?

I want to find the location (s) of a specific item in a list of lists. It should return a list of tuples, where each tuple represents indexes for a particular instance of the element. For example:

list = [['1', '2', '4', '6'], ['7', '0', '1', '4']]
getPosition('1')  #returns [(0, 0), (1, 2)]
and getPosition('7') #returns [(1,0)]
+5
source share
9 answers

If you want something that will be

  • find duplicates and
  • handle nested lists (lists of list lists ...)

you can do something like the following:

def get_positions(xs, item):
    if isinstance(xs, list):
        for i, it in enumerate(xs):
            for pos in get_positions(it, item):
                yield (i,) + pos
    elif xs == item:
        yield ()

Testing:

>>> xs = [['1', '2', '4', '6'],
...       ['7', '0', '1', '4'],
...       [ [ '0', '1', '1'], ['1']]
...       ]
>>> print list(get_positions(xs, '1'))
[(0, 0), (1, 2), (2, 0, 1), (2, 0, 2), (2, 1, 0)]
+7
source

, , , ( , ). , Python, enumerate():

def getPosition(list, item):
    return [(i, sublist.index(item)) for i, sublist in enumerate(list)]

: . @scribble /.

+5
def getPosition(list, item):
    return [(i, sublist.index(item)) for i, sublist in enumerate(list) 
                                                      if item in sublist]
+3
def get_positions(xs, target):
    return [(i,e.index(target)) for i,e in enumerate(xs)]

. , ,

class SomeClass:
    def __init__(self):
        self.xs = [['1','2','4','6'], ['7','0','1','4']]

    def get_positions(self, target):
        return [(i,e.index(target)) for i,e in enumerate(self.xs)]


model = SomeClass()
model.get_position(1)    # returns [(0,0), (1,2)]

, , . , .

+2

, , . , .

xs = [['1', '2', '4', '6'], ['7', '0', '1', '4']]
def get_positions(xs, item):
    for i, xt in enumerate( xs ):
        try: # trying beats checking
            yield (i, xt.index(item))
        except ValueError: 
            pass

print list(get_positions(xs, '1'))
print list(get_positions(xs, '6'))

# Edit for fun: The one-line version, without try:

get_positions2 = lambda xs,item: ((i,xt.index(item)) for  i, xt in enumerate(xs) if item in xt)

print list(get_positions2(xs, '1'))
print list(get_positions2(xs, '6'))
+2

python, . ?, + * , ? , + - , * . :

from matching import match

match(['?', 2, 3, '*'], [1, 2, 3, 4, 5])
=> [1, [4, 5]]

match([1, 2, 3], [1, 2, 4])
=> MatchError: broken at 4

match([1, [2, 3, '*']], [1, [2, 3, 4]])
=> [[4]]

match([1, [2, 3, '*']], [1, [2, 3, 4]], True)
=> [1, 2, 3, [4]]

: http://www.artfulcode.net/wp-content/uploads/2008/12/matching.zip

0

try..except, ,

[['1', '1', '1', '1'], ['7', '0', '4']]


[(0, 0), (0, 1), (0, 2), (0, 3)] 


def getPosition1(l, val):
  for row_nb, r in enumerate(l):
      for col_nb in (x for x in xrange(len(r)) if r[x] == val):
         yield row_nb, col_nb
0

, , :

    >>> value = '1'
    >>> l = [['1', '2', '3', '4'], ['3', '4', '5', '1']]
    >>> m = []
    >>> for i in range(len(l)):
    ...  for j in range(len(l[i])):
    ...   if l[i][j] == value:
    ...    m.append((i,j))
    ...
    >>> m
    [(0, 0), (1, 3)]
0

, .

def getPosition(lists,item):
    positions = []
    for i,li in enumerate(lists):
        j = -1
        try:
            while True:
                j = li.index(item,j+1)
                positions.append((i,j))
        except ValueError:
            pass
    return positions

l = [['1', '2', '4', '6'], ['7', '0', '1', '4']]
getPosition(l,'1')  #returns [(0, 0), (1, 2)]
getPosition(l,'9') # returns []

l = [['1', '1', '1', '1'], ['7', '0', '1', '4']]
getPosition(l,'1')  #returns [(0, 0), (0, 1), (0,2), (0,3), (1,2)]
0

More articles:


All Articles