Question

I have two python lists as follow:

ListA = [a1,a2,a1,a3,a2,a4,a5,a4]
ListB = [b1,b2,b1,b3,b2,b4,b5,b4]

What I want is to find the equal elements in the two lists and print them in a file. I have found the equal elements in lists and add them to two new lists as follow:

[a1,a2,a4]
[b1,b2,b4]

I want to compare some parameters with elements in ListA and if an element in ListA and the parameter is equal print the corresponding element in ListB. I do this as follow.

for i,j in enumerate(ListA):
    if j == paramname:
        filelines.append('%sTransferSourceName = "%s"\n'%(indent,ListB[i]))

My problem is that the element are not in the order for ListB. It is added like below:

b2,b4,b1

So the whole order get mixed up.
Note that the number of letters in each element in the lists may differ.

Here is the code I have done so far:

def ProcessLinks():

duplicates = [x for x in linkparamArray if linkparamArray.count(x) > 1]

linkstemp = list(set(duplicates))
for i in linkstemp:

    links.append(i)

def ProcessLinks2():

duplicates2 = [x for x in linkparameterArray if linkparameterArray.count(x) > 1]

linkstemp2 = list(set(duplicates2))
for j in linkstemp2:

    linkparameters.append(j)

And here is the comparing code:

paramname = a1

for i,j in zip(linkparameters,links):

                if i == paramname:
                    filelines.append('%s         TransferSourceName = "%s"\n(indent,j))

Answer 1

You can use collections.Counter to determine duplicate elements.

>>> ListA = ['a1','a2','a1','a3','a2','a4','a5','a4']
>>> ListB = ['b1','b2','b1','b3','b2','b4','b5','b4']
>>> cB=collections.Counter(ListB)
>>> cA=x=collections.Counter(ListA)
>>> [i for i in cA if cA[i]>1]
['a1', 'a2', 'a4']
>>> [i for i in cB if cB[i]>1]
['b4', 'b1', 'b2']

As per the Comment of OP as the order is important than the following solution might work using (OrderedDict)[http://docs.python.org/library/collections.html#collections.OrderedDict]

dB=collections.OrderedDict()
dA=collections.OrderedDict()
>>> for a in ListB:
    dB.setdefault(a,0)
    dB[b]+=1

>>> for b in ListB:
    dB.setdefault(b,0)
    dB[b]+=1

>>> [i for i in dA if dA[i]>1]
['a1', 'a2', 'a4']
>>> [i for i in dB if dB[i]>1]
['b1', 'b2', 'b4']