Python sorting 2D array by the first element (not unique)

Question

I have a very big 2D array where the second elements are not unique. Something like this:

list = [ ['text43','value43'], 
         ['text23','value23'], 
         ['text12','value12'],
         ['text43','different_val_43'],
         ['text12','another_value12'], 
         ['text04','value04'], 
         ['text43','anohter_value43'] ]

I would like to sort it by the first element but not in alphabetical order, just in the order of appearance of first element. Desired output:

list = [ ['text43','value43'],
         ['text43','different_val_43'],
         ['text43','anohter_value43'],
         ['text23','value23'],
         ['text12','value12'],
         ['text12','another_value12'],
         ['text04','value04'] ]

Hello @Birbal, you'll need to add some code that you have already tried to make work. Have you tried anything? — gkapellmann
– gkapellmann, Commented Nov 13, 2018 at 13:09
Do not use list as the variable name of a python list. @BearBrown 's answer looks right. — Charles Landau
– Charles Landau, Commented Nov 13, 2018 at 13:11
Thanks @CharlesLandau ...actually was just an example, I have not named it list. — Birbal
– Birbal, Commented Nov 13, 2018 at 13:51

Eugene Yarmash · Accepted Answer · 2018-11-13 13:43:17Z

3

You can use a custom sorting function that would return the index at which the first element of a sublist is first found, e.g.:

lst = [['text43','value43'],
       ['text23','value23'],
       ['text12','value12'],
       ['text43','different_val_43'],
       ['text12','another_value12'],
       ['text04','value04'],
       ['text43','anohter_value43']]

d = {}
for i, item in enumerate(lst):
    if item[0] not in d:
        d[item[0]] = i

lst.sort(key=lambda item: d[item[0]])
print(lst)

Output:

[['text43', 'value43'],
 ['text43', 'different_val_43'],
 ['text43', 'anohter_value43'],
 ['text23', 'value23'],
 ['text12', 'value12'],
 ['text12', 'another_value12'],
 ['text04', 'value04']]

edited Nov 13, 2018 at 13:43

answered Nov 13, 2018 at 13:14

Eugene Yarmash

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Srce Cde · Accepted Answer · 2018-11-29 18:10:22Z

0

Look if this helps. Using sorted()

lst = [ ['text43','value43'], 
         ['text23','value23'], 
         ['text12','value12'],
         ['text43','different_val_43'],
         ['text12','another_value12'], 
         ['text04','value04'], 
         ['text43','anohter_value43'] ]

sorted(lst, reverse=True)

Output:

[['text43', 'value43'],
 ['text43', 'different_val_43'],
 ['text43', 'anohter_value43'],
 ['text23', 'value23'],
 ['text12', 'value12'],
 ['text12', 'another_value12'],
 ['text04', 'value04']]

edited Nov 29, 2018 at 18:10

answered Nov 13, 2018 at 14:11

Srce Cde

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