CODEWITHSUNDEEP
pythonlambda
Gary
Gary

Reputation: 2167

How to convert this lambda command to a function in Python?

How could I convert the following line of code using a lambda command into a function by itself?

I am struggling to get the hang of lambda, and wanted to apply it to an example I found. I am confused about how to convert the x and y when I put it in it's own function, like def sortedList(myList)

The line with the lambda is as follows:

myList = [[1,2],[19,20],[2,3]]    
listNums = sorted(myList, 
                      sortList = lambda x,y: x[0] + y[0] if x[0] == y[0] else y[1] - x[1])

Upvotes: 0

Views: 71

Answers (1)

Paul Becotte
Paul Becotte

Reputation: 9977

listNums = sorted(myList, 
                  sortList = lambda x,y: x[0] + y[0] if x[0] == y[0] else y[1] - x[1])

is equivalent to

def funcname(x,y):
    return x[0] + y[0] if x[0] == y[0] else y[1] - x[1]

listNums = sorted(myList, sortList=funcname)

However, that is not the correct syntax for sorted - it should be 

listNums = sorted(mylist, cmp=funcname)

To address your comment, sorted uses the cmp function to sort the elements of your list. In your question, your list is [[1,2],[19,20],[2,3]]. The basic question is, which comes first [1,2] or [19,20]? Because that question could be answered nearly infinite different ways, it lets you provide the answer with a cmp function. In that case, to decide which of those pairs comes first, sorted will run cmp(x=[1,2], y=[19,20]). If the value is > 0, it assumes x is higher, if it is < 0 it considers y as higher, and if the return value is 0 it figures they are the same value.

The example you chose seems a weird way to do comparisons... if the first values are equal, return the sum of the first values? If they are both positive, then x will always be higher, if they are both negative, y will always be higher. If they aren't equal, sort solely based on the second value.

Upvotes: 1

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