Printing only one index of a list

[shanazzle]

If i had a list of lists, for example:

list = [ [2,3], [4,5], [2,5], [9,2], [3,2]]

how can i write a function that only writes out index[1] of each list in the list?

i need the output to contain 3,5,4,2,2

and then my final goal is to create a loop that goes through the major list and only print out index[0] of the minor lists if they are not in index[1], so in this case, 4 and 9. I tried using a loop in a loop, but its not working. any ideas?

[bartonc]

If i had a list of lists, for example:

list = [ [2,3], [4,5], [2,5], [9,2], [3,2]]

how can i write a function that only writes out index[1] of each list in the list?

i need the output to contain 3,5,4,2,2

and then my final goal is to create a loop that goes through the major list and only print out index[0] of the minor lists if they are not in index[1], so in this case, 4 and 9. I tried using a loop in a loop, but its not working. any ideas?

[CODE=python]
>>> aList = [[2,3], [4,5], [2,5], [9,2], [3,2]]
>>> print [item[1] for item in aList]
[3, 5, 5, 2, 2]
>>> [/CODE]

[bartonc]

[CODE=python]
>>> aList = [[2,3], [4,5], [2,5], [9,2], [3,2]]
>>> print [item[1] for item in aList]
[3, 5, 5, 2, 2]
>>> [/CODE]

This will strip the braces off the ends:[CODE=python]
>>> print str([item[1] for item in aList])[1:-1]
3, 5, 5, 2, 2
>>> [/CODE]

[shanazzle]

but then could i actually put that output into a list? like, have all the index[1]'s in a list so that i could use it to search back through and remove any index[0] values that are also in index[1]?

[dazzler]

If i had a list of lists, for example:

list = [ [2,3], [4,5], [2,5], [9,2], [3,2]]

how can i write a function that only writes out index[1] of each list in the list?

my version ^_^

do not use "list" as your list's variable name

so, in your example
list[0] = [2,3]
list[1] = [4,5] ....
so:
list[0][0] = 2
list[0][1] = 3
list[1][0] = 4
list[1][1] = 5

the loop:
[code=python]

a_list = [ [2,3], [4,5], [2,5], [9,2], [3,2]]

index = 0
while index != len(a_list): #len(a_list) lenght of the list
print a_list[index][1] #prints a_list[0][1],[1][1],[2][1],etc...
index += 1
[/code]

[dazzler]

list = [ [2,3], [4,5], [2,5], [9,2], [3,2]]

and then my final goal is to create a loop that goes through the major list and only print out index[0] of the minor lists if they are not in index[1], so in this case, 4 and 9. I tried using a loop in a loop, but its not working. any ideas?

I don't understand this one, how you get 4 & 9 ? uhm, can you explain more please =)

[shanazzle]

I don't understand this one, how you get 4 & 9 ? uhm, can you explain more please =)

because 4 and 9 are the only numbers that appear in index[0] and do not appear in index[1], does that make sense?

[dazzler]

oh, it is searching the whole list for duplicates, for each index[0] values, now I understand =D

here's the code =)
I have used index[0] & index[1] names in comments to make it maybe a little clearer for you

[code=python]
list_a = [[2,3],[4,5],[2,5],[9,2],[3,2]]
new_list = []

index1 =0
while index1 != len(list_a): #this is looping "index[0]" values

index2 = 0
samevalue = 0 #"reseting" this value for the next round
while index2 != len(list_a): #this is looping "index[1]" values

if list_a[index1][0] == list_a[index2][1]: #checking if we have same number in "index[0]" & "index[1]"
samevalue = 1 #let's remember that there were same number

index2 += 1 #let's try different "index[1]" value

if samevalue == 0: #if we didn't find pair for the number, samevalue is still 0
new_list.append (list_a[index1][0]) # .append saves the value to new list (adds it to the end of list)

index1 += 1 #trying the next "index[0]"

print new_list
[/code]

[bvdet]

This method uses list comprehensions:[code=Python]>>> aList = [[2,3], [4,5], [2,5], [9,2], [3,2]]
>>> prntList = [item[1] for item in aList]
>>> print ", ".join([str(item) for item in prntList])
3, 5, 5, 2, 2
>>> print ", ".join([str(item[0]) for item in aList if item[0] not in prntList])
4, 9
>>> [/code]

[ghostdog74]

unorthodox way:

>>> str(list).replace("[","").replace("]","").split(",")[1::2]
[' 3', ' 5', ' 5', ' 2', ' 2']