Python dictionary Get list of values for list of keys

Question

Is there a built-in quick way to use a list of keys to a dictionary to get a list of corresponding items   For instance I have    gt  gt  gt  mydict     one   1   two   2   three   3   gt  gt  gt  mykeys     three    one     How can I use mykeys to get the corresponding values in the dictionary as a list    gt  gt  gt  mydict WHAT GOES HERE mykeys   3  1

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Try This   mydict     one   1   two   2   three   3  mykeys     three    one   ten   newList  mydict k  for k in mykeys if k in mydict  print newList  3  1

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reduce lambda x y  mydict get y  and x append mydict y   or x  mykeys       incase there are keys not in dict

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A couple of other ways than list-comp    Build list and throw exception if key not found  map mydict   getitem    mykeys  Build list with None if key not found  map mydict get  mykeys    Alternatively  using operator itemgetter can return a tuple   from operator import itemgetter myvalues   itemgetter  mykeys  mydict    use  list       if list is required   Note  in Python3  map returns an iterator rather than a list  Use list map       for a list

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A list comprehension seems to be a good way to do this    gt  gt  gt   mydict x  for x in mykeys   3  1

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Here are three ways   Raising KeyError when key is not found   result    mapping k  for k in iterable    Default values for missing keys   result    mapping get k  default value  for k in iterable    Skipping missing keys   result    mapping k  for k in iterable if k in mapping

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new dict    x  v for x  v in mydict items   if x in mykeys

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Or just mydict keys   That s a builtin method call for dictionaries  Also explore mydict values   and mydict items        Ah  OP post confused me

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Try this   mydict     one   1   two   2   three   3  mykeys     three    one     if there are many keys  use a set   mydict k  for k in mykeys    gt   3  1

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A little speed comparison   Python 2 7 11  Anaconda 2 4 1  64-bit    default  Dec  7 2015  14 10 42   MSC v 1500 64 bit  AMD64   on win32 In 1   l    0 1 2 3 2 3 1 2 0  In 2   m    0 10  1 11  2 12  3 13  In 3    timeit  m    for   in l     list comprehension 1000000 loops  best of 3  762 ns per loop In 4    timeit map lambda    m     l     using  map  1000000 loops  best of 3  1 66   s per loop In 5    timeit list m    for   in l     a generator expression passed to a list constructor  1000000 loops  best of 3  1 65   s per loop In 6    timeit map m   getitem    l  The slowest run took 4 01 times longer than the fastest  This could mean that an intermediate result is being cached  1000000 loops  best of 3  853 ns per loop In 7    timeit map m get  l  1000000 loops  best of 3  908 ns per loop In 33   from operator import itemgetter In 34    timeit list itemgetter  l  m   The slowest run took 9 26 times longer than the fastest  This could mean that an intermediate result is being cached  1000000 loops  best of 3  739 ns per loop   So list comprehension and itemgetter are the fastest ways to do this   UPDATE  For large random lists and maps I had a bit different results   Python 2 7 11  Anaconda 2 4 1  64-bit    default  Dec  7 2015  14 10 42   MSC v 1500 64 bit  AMD64   on win32 In 2   import numpy random as nprnd l   nprnd randint 1000  size 10000  m   dict      nprnd rand    for   in range 1000    from operator import itemgetter import operator f   operator itemgetter  l   timeit f m   timeit list itemgetter  l  m    timeit  m    for   in l     list comprehension  timeit map m   getitem    l   timeit list m    for   in l     a generator expression passed to a list constructor   timeit map m get  l   timeit map lambda    m     l  1000 loops  best of 3  1 14 ms per loop 1000 loops  best of 3  1 68 ms per loop 100 loops  best of 3  2 ms per loop 100 loops  best of 3  2 05 ms per loop 100 loops  best of 3  2 19 ms per loop 100 loops  best of 3  2 53 ms per loop 100 loops  best of 3  2 9 ms per loop   So in this case the clear winner is f   operator itemgetter  l   f m   and clear outsider  map lambda    m     l    UPDATE for Python 3 6 4   import numpy random as nprnd l   nprnd randint 1000  size 10000  m   dict      nprnd rand    for   in range 1000    from operator import itemgetter import operator f   operator itemgetter  l   timeit f m   timeit list itemgetter  l  m    timeit  m    for   in l     list comprehension  timeit list map m   getitem    l    timeit list m    for   in l     a generator expression passed to a list constructor   timeit list map m get  l    timeit list map lambda    m     l  1 66 ms    74 2   s per loop  mean    std  dev  of 7 runs  1000 loops each  2 1 ms    93 2   s per loop  mean    std  dev  of 7 runs  100 loops each  2 58 ms    88 8   s per loop  mean    std  dev  of 7 runs  100 loops each  2 36 ms    60 7   s per loop  mean    std  dev  of 7 runs  100 loops each  2 98 ms    142   s per loop  mean    std  dev  of 7 runs  100 loops each  2 7 ms    284   s per loop  mean    std  dev  of 7 runs  100 loops each  3 14 ms    62 6   s per loop  mean    std  dev  of 7 runs  100 loops each    So  results for Python 3 6 4 is almost the same

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Following closure of  Python  efficient way to create a list from dict values with a given order   Retrieving the keys without building the list   from   future   import  absolute import  division  print function                          unicode literals   import collections   class DictListProxy collections Sequence       def   init   self  klist  kdict   args    kwargs           super DictListProxy  self    init    args    kwargs          self klist   klist         self kdict   kdict      def   len   self           return len self klist       def   getitem   self  key           return self kdict self klist key     myDict     age    value1    size    value2    weigth    value3   order list     age    weigth    size    dlp   DictListProxy order list  myDict   print     join dlp   print   print dlp 1     The output   value1 value3 value2  value3   Which matches the order given by the list

User · Answer

Pandas does this very elegantly  though ofc list comprehensions will always be more technically Pythonic  I don t have time to put in a speed comparison right now  I ll come back later and put it in    import pandas as pd mydict     one   1   two   2   three   3  mykeys     three    one   temp df   pd DataFrame   append mydict    You can export DataFrames to a number of formats  using a list here   temp df mykeys  values 0    Returns  array   3    1       If you want a dict then use this instead    temp df mykeys  to dict orient  records   0    Returns    one   1 0   three   3 0

[python] Python dictionary: Get list of values for list of keys

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