Question

I need to see if 2 items from a list appears in another list, and if they do, compare the items by their position in the other list. Example in pseudo code:

j=0
for x in mylist #loop through the list
    i=0
    for y in mylist #loop through the list again to compare items
        if index of mylist[j] > index of mylist[i] in list1 and list2:
            score[i][j] = 1 #writes the score to a 2d array(numpy) called score
            i=i+1
        else: 
            score[i][j]=0
            i=i+1
j=j+1

Sample Narrative Description:

Names = [John, James, Barry, Greg, Jenny]
Results1 = [James, Barry, Jenny, Greg, John]
Results2 = [Barry, Jenny, Greg, James, John]

loop through Names for i
    loop through Names for j
        if (index value for john) > (index value for james) in results1 and 
           (index value for john) > (index value for james) results2:
            score[i][j] = 1

Can someone please point me in the right direction? I’ve been looking at numerous list, array and .index tutorials but nothing seems to answer my question

Answer 1

Convert your list2 to a dictionary that encodes the position given an item:

dic2 = dict((item,i) for i,item in enumerate(list2))

Now you can test for something being in the list by using x in dic2 and y in dic2 and use dic2[x] to get it’s index in the list.

Edit: It goes against my better instincts, but here’s the complete code. The first part is using what I showed above, turning a simple list into a lookup for the index. Next comes the standard if unintuitive way of initializing a 2D list. This is followed by your loops, using the ever handy enumerate function to assign an index to each name in the list.

Names = ['John', 'James', 'Barry', 'Greg', 'Jenny']
Results1 = ['James', 'Barry', 'Jenny', 'Greg', 'John']
Results2 = ['Barry', 'Jenny', 'Greg', 'James', 'John']

Order1 = dict((name,order) for order,name in enumerate(Results1))
Order2 = dict((name,order) for order,name in enumerate(Results2))

score = [[0]*len(Names) for y in range(len(Names))]

for i,name1 in enumerate(Names):
    for j,name2 in enumerate(Names):
        if name1 in Order1 and name2 in Order1 and Order1[name1] > Order1[name2] and name1 in Order2 and name2 in Order2 and Order2[name1] > Order2[name2]:
            score[i][j] = 1