Python filter lambda if condition

lambda x : x > 10 and x < 20

This lambda function does the same stuff as above i..e checks if given number lies between 10 to 20. Now let’s use this function to check some values i.e.

# Lambda function to check if a given vaue is from 10 to 20.
check = lambda x : x > 10 and x < 20

# Check if given numbers are in range using lambda function
print[check[12]]
print[check[3]]
print[check[24]]

Output:

True
False
False

Using filter[] function with a conditional lambda function [with if else]

filter[] function accepts a callback[] function and a list of elements. It iterates over all elements in list and calls the given callback[] function
on each element. If callback[] returns True then it appends that element in the new list. In the end it returns a new list of filtered elements only.

Suppose we have a list of numbers i.e.

# List of numbers
listofNum = [1,3,33,12,34,56,11,19,21,34,15]

Now let’s use filter[] function to filter numbers between 10 to 20 only by passing a conditional lambda function [with if else] to it i.e.

# Filter list of numbers by keeping numbers from 10 to 20 in the list only
listofNum = list[filter[lambda x : x > 10 and x < 20, listofNum]]
print['Filtered List : ', listofNum]

Output:

Filtered List :  [12, 11, 19, 15]

it uses the passed lambda function to filter elements and in the end returns list of elements that lies between 10 to 20,

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Using if, elif & else in a lambda function

Till now we have seen how to use if else in a lambda function but there might be cases when we need to check multiple conditions in a lambda function. Like we need to use if , else if & else in a lambda function. We can not directly use elseif in a lambda function. But we can achieve the same effect using if else & brackets i.e.

lambda  :  if  [  if  else ]

Let’s see how to do that,

Create a lambda function that accepts a number and returns a new number based on this logic,

• If the given value is less than 10 then return by multiplying it by 2
• else if it’s between 10 to 20 then return multiplying it by 3
• else returns the same un-modified value

# Lambda function with if, elif & else i.e.
# If the given value is less than 10 then Multiplies it by 2
# else if it's between 10 to 20 the multiplies it by 3
# else returns the unmodified same value
converter = lambda x : x*2 if x < 10 else [x*3 if x < 20 else x]

Let’s use this lambda function,

print['convert 5 to : ', converter[5]]
print['convert 13 to : ', converter[13]]
print['convert 23 to : ', converter[23]]

Output:

convert 5 to :  10
convert 13 to :  39
convert 23 to :  23

Complete example is as follows,

def main[]:
    print['*** Using if else in Lambda function ***']
    # Lambda function to check if a given vaue is from 10 to 20.
    test = lambda x : True if [x > 10 and x < 20] else False

    # Check if given numbers are in range using lambda function
    print[test[12]]
    print[test[3]]
    print[test[24]]

    print['*** Creating conditional lambda function without if else ***']

    # Lambda function to check if a given vaue is from 10 to 20.
    check = lambda x : x > 10 and x < 20

    # Check if given numbers are in range using lambda function
    print[check[12]]
    print[check[3]]
    print[check[24]]

    print['*** Using filter[] function with a conditional lambda function [with if else] ***']

    # List of numbers
    listofNum = [1,3,33,12,34,56,11,19,21,34,15]
    print['Original List : ', listofNum]

    # Filter list of numbers by keeping numbers from 10 to 20 in the list only
    listofNum = list[filter[lambda x : x > 10 and x < 20, listofNum]]
    print['Filtered List : ', listofNum]

    print['*** Using if, elif & else in Lambda function ***']

    # Lambda function with if, elif & else i.e.
    # If the given value is less than 10 then Multiplies it by 2
    # else if it's between 10 to 20 the multiplies it by 3
    # else returns the unmodified same value
    converter = lambda x : x*2 if x < 10 else [x*3 if x < 20 else x]

    print['convert 5 to : ', converter[5]]
    print['convert 13 to : ', converter[13]]
    print['convert 23 to : ', converter[23]]

if __name__ == '__main__':
    main[]

Output:

*** Using if else in Lambda function ***
True
False
False
*** Creating conditional lambda function without if else ***
True
False
False
*** Using filter[] function with a conditional lambda function [with if else] ***
Original List :  [1, 3, 33, 12, 34, 56, 11, 19, 21, 34, 15]
Filtered List :  [12, 11, 19, 15]
*** Using if, elif & else in Lambda function ***
convert 5 to :  10
convert 13 to :  39
convert 23 to :  23