Slicing Tuples in a List of Lists in Python-CodePudding

I have tuples in a list of lists and would like to extract only some elements in the tuple. Sample of the input data is below.

# input 
[[('ab', 0.026412873688749918), ('dc', 0.016451082731822664), ('on', 0.014278088125928066),
  ('qc', 0.009752817881775656), ('mn', 0.008332886637563352), ('nt', 0.008250535392602258),
  ('nsw', 0.006874273287824427), ('bar', 0.005878684829852004), ('tor', 0.005741627328513831),
  ('wds', 0.004119216502907735)],
 [('nb', 0.03053649661493629), ('ns', 0.01925207174326825), ('ham', 0.016207228280183325),
  ('bra', 0.013390785663058102), ('nia', 0.00878166482558038), ('knxr', 0.004648856466085521),
  ('nwm', 0.004463444159552605), ('md', 0.004377821331080258), ('ut', 0.004165890522922745),
  ('va', 0.0037484060754341083)]]

What I am trying to do is get the first items in the tuples.

# output
[['ab', 'dc', 'on', 'qc', 'mn', 'nt', 'nsw', 'bar', 'tor', 'wds'],
['nb', 'ns', 'ham', 'bra', 'nia', 'knxr', 'nwm', 'md', 'ut', 'va']]

CodePudding user response：

input = [
          [('ab', 0.026412873688749918), ('dc', 0.016451082731822664), ('on', 0.014278088125928066),
          ('qc', 0.009752817881775656), ('mn', 0.008332886637563352), ('nt', 0.008250535392602258),
          ('nsw', 0.006874273287824427), ('bar', 0.005878684829852004), ('tor', 0.005741627328513831),
          ('wds', 0.004119216502907735)],
         
         [('nb', 0.03053649661493629), ('ns', 0.01925207174326825), ('ham', 0.016207228280183325),
          ('bra', 0.013390785663058102), ('nia', 0.00878166482558038), ('knxr', 0.004648856466085521),
          ('nwm', 0.004463444159552605), ('md', 0.004377821331080258), ('ut', 0.004165890522922745),
          ('va', 0.0037484060754341083)]
        ]

As illustrated in the comments you can use list comprehensions to achieve this:

[[idx for idx, val in x] for x in input]

# Result
[['ab', 'dc', 'on', 'qc', 'mn', 'nt', 'nsw', 'bar', 'tor', 'wds'],
 ['nb', 'ns', 'ham', 'bra', 'nia', 'knxr', 'nwm', 'md', 'ut', 'va']]

A more complex way to achieve this would be to use zip() to separate the first elements from the second elements of the tuples as shown below:

[('ab', 'dc', 'on', 'qc', 'mn', 'nt', 'nsw', 'bar', 'tor', 'wds'),
(0.026412873688749918,0.016451082731822664,0.014278088125928066,0.009752817881775656,0.008332886637563352,0.008250535392602258,0.006874273287824427,0.005878684829852004,0.005741627328513831,0.004119216502907735)]

This approach can be done using:

[list(list(zip(*x))[0]) for x in input]

# Result
[['ab', 'dc', 'on', 'qc', 'mn', 'nt', 'nsw', 'bar', 'tor', 'wds'],
 ['nb', 'ns', 'ham', 'bra', 'nia', 'knxr', 'nwm', 'md', 'ut', 'va']]

CodePudding user response：

You can use loop or list comprehension to do this.

The input data is list of lists that contains tuples. Access the first element of the tuple by using tuple[0] and save it into an empty list like this:-

input_data = [
        [('ab', 0.026412873688749918), ('dc', 0.016451082731822664), ('on', 0.014278088125928066),
          ('qc', 0.009752817881775656), ('mn', 0.008332886637563352), ('nt', 0.008250535392602258),
          ('nsw', 0.006874273287824427), ('bar', 0.005878684829852004), ('tor', 0.005741627328513831),
          ('wds', 0.004119216502907735)],
         [('nb', 0.03053649661493629), ('ns', 0.01925207174326825), ('ham', 0.016207228280183325),
          ('bra', 0.013390785663058102), ('nia', 0.00878166482558038), ('knxr', 0.004648856466085521),
          ('nwm', 0.004463444159552605), ('md', 0.004377821331080258), ('ut', 0.004165890522922745),
          ('va', 0.0037484060754341083)]
    ]
    
data_list = []
for x in input_data:
    d_list = []
    for y in x:
        d_list.append(y[0])
        
    data_list.append(d_list)

# Result...
[['ab', 'dc', 'on', 'qc', 'mn', 'nt', 'nsw', 'bar', 'tor', 'wds'],
 ['nb', 'ns', 'ham', 'bra', 'nia', 'knxr', 'nwm', 'md', 'ut', 'va']]

Using list comprehension:- It is a shorthand way to write the for loop above by removing append() method and the initial empty lists.

data_list = [ [y[0] for y in x] for x in input_data ]
    
# Result...
[['ab', 'dc', 'on', 'qc', 'mn', 'nt', 'nsw', 'bar', 'tor', 'wds'],
['nb', 'ns', 'ham', 'bra', 'nia', 'knxr', 'nwm', 'md', 'ut', 'va']]