How to create a lambda function from a tuple of values

Question

The basic objective is to sort a list of lists based on a field in the inner lists. So i have the below Python code for doing it:

import sys

def sort_cleaned_data(data, fields=None):
    if not isinstance(fields, tuple):
        raise ValueError("Argument to the function has to be a tuple")
    else:
        if all(list(map(lambda x:isinstance(x, int), fields))):
            sorted_data = sorted(data, key=lambda x:(x[2],x[1]))
            return sorted_data
        else:
            raise ValueError("All the values inside the fields tuple have to be integers")


data = [
["John", 34, 2],
["Ashley", 30, 2],
["Peter", 28, 5],
["Bill", 29, 5],
["Jennifer", 65, 4],
["Laura", 33, 3]
]
try:
    sorted_data = sort_cleaned_data(data, fields=(2,1))
except ValueError as e:
    print(e)
    sys.exit(1)

for d in sorted_data:
    print(d)

In the function sort_cleaned_data i have the fields tuple which contain the fields of the inner array on which to sort. So i have to dynamically generate the function : key=lambda x:(x[2],x[1]) based on the fields list.

I think this is the case of eval in Python but i am not sure how to do this . Can someone please help me here .

Many thanks in advance.

Vikrant Sharma · Accepted Answer · 2018-10-22 08:30:08Z

2

Using a comprehension:

sorted(data, key=lambda x: tuple(x[i] for i in fields))

Now fields can be arbitrary in size and values, provided x (inner list) has enough elements to not raise IndexError.

answered Oct 22, 2018 at 8:30

Vikrant Sharma

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Comments

Duncan · Accepted Answer · 2018-10-22 08:35:35Z

1

This is overly complicated. Just use operator.itemgetter to create your key function.

import operator
def sort_cleaned_data(data, fields=None):
   return sorted(data, key=operator.itemgetter(*fields))

data = [
["John", 34, 2],
["Ashley", 30, 2],
["Peter", 28, 5],
["Bill", 29, 5],
["Jennifer", 65, 4],
["Laura", 33, 3]
]

sorted_data = sort_cleaned_data(data, fields=(2,1))
for d in sorted_data:
    print(d)

Output:

['Ashley', 30, 2]
['John', 34, 2]
['Laura', 33, 3]
['Jennifer', 65, 4]
['Peter', 28, 5]
['Bill', 29, 5]

answered Oct 22, 2018 at 8:35

Duncan

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Comments

bruno desthuilliers · Accepted Answer · 2018-10-22 08:30:33Z

0

You're making it much more complicated than it has to be:

def sort_cleaned_data(data, fields):
    return sorted(data, key=lambda x: (x[fields[0]], x[fields[1]]))


data = [
["John", 34, 2],
["Ashley", 30, 2],
["Peter", 28, 5],
["Bill", 29, 5],
["Jennifer", 65, 4],
["Laura", 33, 3]
]

sorted_data = sort_cleaned_data(data, fields=(2,1))
for d in sorted_data:
    print(d)

answered Oct 22, 2018 at 8:30

bruno desthuilliers

78.3k6 gold badges102 silver badges129 bronze badges

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