Raw Python - Filters

Filtering basically just helps filter out certain values from a list. You take a function that returns a boolean value - true or false and filters out the values that return false when you apply that function to an item and keeps those that return True.



In [1]:

    
x = range(10)



In [2]:

    
x









    Out[2]:





range(0, 10)



In [3]:

    
def divis_by_2(num):
    return num % 2 == 0



In [4]:

    
divis_by_2(2)









    Out[4]:





True



In [5]:

    
divis_by_2(3)









    Out[5]:





False



In [16]:

    
list(map(divis_by_2, x))









    Out[16]:





[True, False, True, False, True, False, True, False, True, False]



In [17]:

    
list(filter(divis_by_2, x))









    Out[17]:





[0, 2, 4, 6, 8]



In [8]:

    
test_list = [
"hello",
"x,y,z. i like this.",
"this is two xx",
"this, x, here x is, here it is againx"
]



In [9]:

    
def has_x(my_string):
    return my_string.count("x") >= 2



In [10]:

    
has_x("hello")









    Out[10]:





False



In [11]:

    
has_x("xxhello")









    Out[11]:





True



In [18]:

    
list(filter(has_x, test_list))









    Out[18]:





['this is two xx', 'this, x, here x is, here it is againx']

It acts just like map, it maps values from true to false and helps us only get those that meet the criteria



In [14]:

    
list(map(has_x, test_list))









    Out[14]:





[False, False, True, True]



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