key = lambda...... usage?

Question

Hi everyone,

Can someone explain why the below code don't output like that >> [1, 2, 3, 4, 5].

a_list = [3, -4, -2, 5, 1]
f = sorted(a_list, key = lambda x: abs(x))
print(f)

output >> [1, -2, 3, -4, 5]

Thanks in advance.

Answer 1

Let we have a number which is n.abs is a function which gives you distance from 0 to n.
now in your code it sort the number acc. to abs function.so
3 has distance from zero is 3.
-4 has distance from zero is 4
-2 has distance from zero is 2
5 has distance from zero is 5
1 has distance from zero is 1
Now,abs function include the number in list in increasing order of their distance from zero.

1 has first because it distance from zero is 1.
-2 is second because it has distance from zero is 2.
blablabla......

so that's why your output is 1, -2, 3, -4, 5

Answer 2

The lambda in the key is only used to determine the position in the sort, it does not change the value.
What you want is

a_list=[1,-2,-5,4,-3]
f=sorted(map(abs,a_list))
print(f)

Answer 3

hi, it is working correctly. sorted method sorts list using abs method but do not change the list elements.
you can directly pass abs also.

#sorte a list using abs method
l = [-4,-5,1,2,3,6]
print(sorted(l,key=abs))

#sort a list of string using last character
l = ['jaz','dixit','dipak','jaimin','jay']
print(sorted(l,key=(lambda x: x[-1])))