I want to append to a new list , only the tuples in which the third element is the same with the third element of the first tuple

Question

After a sort to a list of tuples, for example:

jen =  (34,54,15) , (34,65,15), (34, 78,89) ...

I am trying to append to a new list only the tuples which contain the third element of the first tuple for instance the new list must contain only:

(34,54,15) 
(34,65,15)

Here is my pseudocode:

   Salvation_array = []
    For lines in  jen:
    Num = 0
    If jen[0] [:-2] = Num:
    Salvation_array.append(Num)

I am really confused with this can you help , suggest something?

Answer 1

You can do that with filter method easily.

In one liner filter call:

array1 = [(34,54,15) , (34,65,15), (34, 78,89)]
array2 = filter(lambda element: element[2] == array[0][2], array)
print array2
[(34, 54, 15), (34, 65, 15)]

You can check the documentation of filter here . So, basically what filter( some_function(e) , array) does it it iterates through each element e of array and test if it satisfies some condition. This check is done using the call some_function(e) . If that function returns True , the element e is kept, otherwise not.

Also, since you mentioned that you are python novice, I guess you might not know about lambda in python. So basically can take them as one liner nameless functions. You can think of following to be equivalent: lambda x: print x and def printit(x): print x; You can check about lambda here

Hope it helps :)

Answer 2

If I understood the requirements correctly, this should do what you want:

jen = (34,54,15), (34,65,15), (34, 78,89)

salvation_army = [j for j in jen if j[2] == jen[0][2]]

print(salvation_army)

# Output:
# [(34, 54, 15), (34, 65, 15)]

It's similar to @Harsh's answer but uses list comprehension rather than filter . (This is a matter of taste.)

Something more along the lines of what you were trying to do:

salvation_army = []
desired_value = jen[0][2]

for line in jen:
    if line[2] == desired_value:
        salvation_army.append(line)