topic Re: How can these two scripts yield different len numbers? in Python Questions

How can these two scripts yield different len numbers?

GeoDev — Wed, 14 Apr 2021 19:37:26 GMT

for i in list1:
    if i in list2:
        inBoth1.append(i)

for i in list2:
    if i in list1:
        inBoth2.append(i)

print(len(inBoth1))
print(len(inBoth2))


For my application, I am using StreetNamesInCountyBlank1 (list1) as one list and trying to see how many match items in another list, StreetNamesCountyBlank2 (list2). However, when I reverse the script like in the example above, I get a significant difference in values.

Re: How can these two scripts yield different len numbers?

Anonymous User — Wed, 14 Apr 2021 19:51:17 GMT

Could be that you have duplicates in one list:

list1 = ['a', 'b', 'c', 'd'] list2 = ['a', 'b', 'c', 'd', 'c', 'aa', 'aaa', 'a', 'c'] inBoth1 = [] inBoth2 = [] for i in list1: if i in list2: inBoth1.append(i) for i in list2: if i in list1: inBoth2.append(i) print(len(inBoth1)) print(len(inBoth2))

gets you 4 and 7 (because of the c's).

Using set on the list you get the same number:

list1 = ['a', 'b', 'c', 'd'] list2 = ['a', 'b', 'c', 'd', 'c', 'aa', 'aaa', 'a', 'c'] inBoth1 = [] inBoth2 = [] for i in set(list1): if i in list2: inBoth1.append(i) for i in set(list2): if i in list1: inBoth2.append(i) print(len(inBoth1)) print(len(inBoth2))

4 and 4

Re: How can these two scripts yield different len numbers?

BlakeTerhune — Wed, 14 Apr 2021 20:10:34 GMT

If you're trying to find the "intersection" of the two lists (values that exist in both), try comparing the lists as sets.

set(list1).intersection(set(list2))

Re: How can these two scripts yield different len numbers?

Tomasz_Tarchalski — Wed, 14 Apr 2021 20:15:23 GMT

I would agree with JeffK, your list must have some duplications.

Another option is to create a dictionary of unique keys (your street name ?) : values (any value, lets say 1).

next looping through second feature class ( cursor) just checking if the value from that feature is in your dictionary or not (if myvalue in mydico.keys()). sth like that:

fields1 = ['field1','field2'] fc1 = StreetNamesInCountyBlank1 mydico = {} # lets assume that my key will be the value from field1 with arcpy.da.SearchCursor(fc1, fields1) as recs: for rec in recs: if rec[0] in mydico: # lets count how many times the same key mydico[rec[0] += 1 else: # the key is first time mydico[rec[0]] = 1 # now lets loop through second feature class fc2 = StreetNamesInCountyBlank2 fields2 = ['field1','field2'] repetition_dico = {} with arcpy.da.SearchCursor(fc2, fields2) as recs: for rec in recs: if rec[0] in mydico.keys(): if rec[0] not in repetition_dico.keys(): repetition_dico[rec[0] = 1 else: # you alredy know that this is repeated, lets add count only repetition_dico[rec[0] += 1 # print results print( len(repetition_dico)) for key, values in repetition_dico.items(): print (key, value)

Re: How can these two scripts yield different len numbers?

JoshuaBixby — Wed, 14 Apr 2021 21:45:45 GMT

Beyond all the good feedback already provided, you never show how your "both" lists are initially created, which leaves the door open to them being different before you even started appending to them.