In Python how do I index a list with another list

Question

I would like to index a list with another list like this  L     a    b    c    d    e    f    g    h   Idx    0  3  7  T   L  Idx     and T should end up being a list containing   a    d    h     Is there a better way than  T      for i in Idx      T append L i    print T   Gives result   a    d    h

User · Answer

T   map lambda i  L i   Idx

User · Answer

I wasn t happy with any of these approaches  so I came up with a Flexlist class that allows for flexible indexing  either by integer  slice or index-list   class Flexlist list       def   getitem   self  keys           if isinstance keys   int  slice    return list   getitem   self  keys          return  self k  for k in keys    Which  for your example  you would use as   L   Flexlist   a    b    c    d    e    f    g    h    Idx    0  3  7  T   L  Idx    print T       a    d    h

User · Answer

You could also use the   getitem   method combined with map like the following   L     a    b    c    d    e    f    g    h   Idx    0  3  7  res   list map L   getitem    Idx   print res      a    d    h

User · Answer

If you are using numpy  you can perform extended slicing like that    gt  gt  gt  import numpy  gt  gt  gt  a numpy array   a    b    c    d    e    f    g    h     gt  gt  gt  Idx    0  3  7   gt  gt  gt  a Idx  array   a    d    h           dtype   S1        and is probably much faster  if performance is enough of a concern to to bother with the numpy import

User · Answer

T    L i  for i in Idx

User · Answer

My problem  Find indexes of list  L   makelist     Returns a list of different objects La   np array L  dtype   object    add dtype  for c in chunks      L    La c    Since La is array  this works

User · Answer

A functional approach   a    1  A   34  -123   Hello   12  b    0  2  5   from operator import itemgetter  print list itemgetter  b  a     1  34  12

User · Answer

L    a   a   d   d    h   h   index    a   d   h    for keys in index      print L keys     I would use a Dict add desired keys to index

[python] In Python, how do I index a list with another list?

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