Sorting list based on values from another list

Question

I have a list of strings like this   X     a    b    c    d    e    f    g    h    i   Y     0    1    1    0    1    2    2    0    1     What is the shortest way of sorting X using values from Y to get the following output     a    d    h    b    c    e    i    f    g     The order of the elements having the same  key  does not matter  I can resort to the use of for constructs but I am curious if there is a shorter way  Any suggestions

User · Answer

This is an old question but some of the answers I see posted don't actually work because zip is not scriptable. Other answers didn't bother to import operator and provide more info about this module and its benefits here.

There are at least two good idioms for this problem. Starting with the example input you provided:

X = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]
Y = [ 0,   1,   1,   0,   1,   2,   2,   0,   1 ]

Using the "Decorate-Sort-Undecorate" idiom

This is also known as the Schwartzian_transform after R. Schwartz who popularized this pattern in Perl in the 90s:

# Zip (decorate), sort and unzip (undecorate).
# Converting to list to script the output and extract X
list(zip(*(sorted(zip(Y,X)))))[1]                                                                                                                       
# Results in: ('a', 'd', 'h', 'b', 'c', 'e', 'i', 'f', 'g')

Note that in this case Y and X are sorted and compared lexicographically. That is, the first items (from Y) are compared; and if they are the same then the second items (from X) are compared, and so on. This can create unstable outputs unless you include the original list indices for the lexicographic ordering to keep duplicates in their original order.

Using the `operator` module

This gives you more direct control over how to sort the input, so you can get sorting stability by simply stating the specific key to sort by. See more examples here.

import operator    

# Sort by Y (1) and extract X [0]
list(zip(*sorted(zip(X,Y), key=operator.itemgetter(1))))[0]                                                                                                 
# Results in: ('a', 'd', 'h', 'b', 'c', 'e', 'i', 'f', 'g')

User · Answer

Shortest Code   x for   x in sorted zip Y X      Example   X     a    b    c    d    e    f    g    h    i   Y     0    1    1     0    1    2    2    0    1   Z    x for   x in sorted zip Y X    print Z       a    d    h    b    c    e    i    f    g       Generally Speaking   x for    x in sorted zip Y X   key lambda pair  pair 0      Explained    zip the two lists  create a new  sorted list based on the zip using sorted    using a list comprehension extract the first elements of each pair from the sorted  zipped list    For more information on how to set use the key parameter as well as the sorted function in general  take a look at this

User · Answer

You can create a pandas Series  using the primary list as data and the other list as index  and then just sort by the index   import pandas as pd pd Series data X index Y  sort index   tolist     output     a    d    h    b    c    e    i    f    g

User · Answer

Also  if you don t mind using numpy arrays  or in fact already are dealing with numpy arrays      here is another nice solution   people     Jim    Pam    Micheal    Dwight   ages    27  25  4  9   import numpy people   numpy array people  ages   numpy array ages  inds   ages argsort   sortedPeople   people inds    I found it here  http   scienceoss com sort-one-list-by-another-list

User · Answer

Here is Whatangs answer if you want to get both sorted lists  python3    X     a    b    c    d    e    f    g    h    i   Y     0    1    1     0    1    2    2    0    1   Zx  Zy   zip    x  y  for x  y in sorted zip Y  X      print list Zx       0  0  0  1  1  1  1  2  2  print list Zy        a    d    h    b    c    e    i    f    g     Just remember Zx and Zy are tuples  I am also wandering if there is a better way to do that   Warning  If you run it with empty lists it crashes

User · Answer

I have created a more general function  that sorts more than two lists based on another one  inspired by  Whatang s answer   def parallel sort  lists               Sorts the given lists  based on the first one       param lists  lists to be sorted       return  a tuple containing the sorted lists                Create the initially empty lists to later store the sorted items     sorted lists   tuple    for   in range len lists           Unpack the lists  sort them  zip them and iterate over them     for t in sorted zip  lists              list items are now sorted based on the first list         for i  item in enumerate t        for each item                sorted lists i  append item        store it in the appropriate list      return sorted lists

User · Answer

list1     a   b   c   d   e   f   g   h   i   list2    0 1 1 0 1 2 2 0 1   output    cur loclist        To get unique values present in list2  list set   set list2    To find the loc of the index in list2   list str      join str s  for s in list2    Location of index in list2 is tracked using cur loclist   0  3  7  1  2  4  8  5  6   for i in list set  cur loc   list str find str i    while cur loc  gt   0      cur loclist append cur loc      cur loc   list str find str i  cur loc 1   print cur loclist   for i in range 0 len cur loclist    output append list1 cur loclist i    print output

User · Answer

Another alternative  combining several of the answers   zip  sorted zip Y X    1    In order to work for python3   list zip  sorted zip B A     1

User · Answer

I actually came here looking to sort a list by a list where the values matched   list a     foo    bar    baz   list b     baz    bar    foo   sorted list b  key lambda x  list a index x       foo    bar    baz

User · Answer

I like having a list of sorted indices  That way  I can sort any list in the same order as the source list  Once you have a list of sorted indices  a simple list comprehension will do the trick   X     a    b    c    d    e    f    g    h    i   Y     0    1    1     0    1    2    2    0    1   sorted y idx list   sorted range len Y   key lambda x Y x   Xs    X i  for i in sorted y idx list    print   Xs    Xs     prints  Xs    a    d    h    b    c    e    i    f    g     Note that the sorted index list can also be gotten using numpy argsort

User · Answer

zip  sort by the second column  return the first column   zip  sorted zip X Y   key operator itemgetter 1    0

User · Answer

Zip the two lists together  sort it  then take the parts you want    gt  gt  gt  yx   zip Y  X   gt  gt  gt  yx   0   a     1   b     1   c     0   d     1   e     2   f     2   g     0   h     1   i     gt  gt  gt  yx sort    gt  gt  gt  yx   0   a     0   d     0   h     1   b     1   c     1   e     1   i     2   f     2   g     gt  gt  gt  x sorted    x for y  x in yx   gt  gt  gt  x sorted   a    d    h    b    c    e    i    f    g     Combine these together to get    x for y  x in sorted zip Y  X

User · Answer

A quick one-liner   list a    5 4 3 2 1  list b    1 1 5 1 75 2 3 3 5 3 75 4 5    Say you want list a to match list b   orderedList    sorted list a  key lambda x  list b index x     This is helpful when needing to order a smaller list to values in larger  Assuming that the larger list contains all values in the smaller list  it can be done

User · Answer

more itertools has a tool for sorting iterables in parallel   Given  from more itertools import sort together   X     a    b    c    d    e    f    g    h    i   Y     0    1    1     0    1    2    2    0    1    Demo  sort together  Y  X   1      a    d    h    b    c    e    i    f    g

User · Answer

The most obvious solution to me is to use the key keyword arg   gt  gt  gt  X     quot a quot    quot b quot    quot c quot    quot d quot    quot e quot    quot f quot    quot g quot    quot h quot    quot i quot    gt  gt  gt  Y     0    1    1     0    1    2    2    0    1   gt  gt  gt  keydict   dict zip X  Y    gt  gt  gt  X sort key keydict get   gt  gt  gt  X   a    d    h    b    c    e    i    f    g    Note that you can shorten this to a one-liner if you care to   gt  gt  gt  X sort key dict zip X  Y   get   As Wenmin Mu and Jack Peng have pointed out  this assumes that the values in X are all distinct  That s easily managed with an index list   gt  gt  gt  Z     quot A quot    quot A quot    quot C quot    quot C quot    quot C quot    quot F quot    quot G quot    quot H quot    quot I quot    gt  gt  gt  Z index   list range len Z     gt  gt  gt  Z index sort key keydict get   gt  gt  gt  Z    Z i  for i in Z index   gt  gt  gt  Z   A    C    H    A    C    C    I    F    G    Since the decorate-sort-undecorate approach described by Whatang is a little simpler and works in all cases  it s probably better most of the time   This is a very old answer

[python] Sorting list based on values from another list

Using the "Decorate-Sort-Undecorate" idiom

Using the `operator` module

Examples related to python

Examples related to list

Examples related to sorting

[python] Sorting list based on values from another list

Using the "Decorate-Sort-Undecorate" idiom

Using the operator module

Examples related to python

Examples related to list

Examples related to sorting

Using the `operator` module