Searching python list using for loop and conditional statements

Question

a = [1,1,1,4,4,4,5]
b = [20150602, 20150603, 20150604, 20150605, 20150606, 20150607,20150608]
c = zip(a,b)

output = []
for i in range(0, len(c)-1):
    if c[i][0] == c[i+1][0] and c[i+1][1] - c[i][1] <= 3:
        output.append(c[i])
print output

This code searches 2 lists using conditionals. If element n == element n+1 in list a AND (element n+1) - (element n)<= 3 in list b .....it prints the results. The problem I'm having is that it cuts off 1 element that should be printing. (ie This code will output

[(1, 20150602), (1, 20150603), (4, 20150605), (4, 20150606)]

but should be outputting

[(1, 20150602), (1, 20150603), (1,20150604), (4, 20150605), (4, 20150606), (4, 20150607)])

Answer 1

See the second append to the output list. :)

In [14]:

a = [1,1,1,4,4,4,5]
b = [20150602, 20150603, 20150604, 20150605, 20150606, 20150607,20150608]
c = zip(a,b)

output = []
for i in range(0, len(c)-1):
    if c[i][0] == c[i+1][0] and c[i+1][1] - c[i][1] <= 3:
        output.append(c[i])
        output.append(c[i+1])
    output = sorted(list(set(output)))
print output



[(1, 20150602), (1, 20150603), (1, 20150604), (4, 20150605), (4, 20150606), (4, 20150607)]

Answer 2

a = [1,1,1,4,4,4,5]
b = [20150602, 20150603, 20150604, 20150605, 20150606, 20150607,20150608]
c = zip(a,b)

output = []
for i in range(0, len(c)-1):
    if c[i][0] == c[i+1][0] and c[i+1][1] - c[i][1] <= 3:
        output.append(c[i])
    elif c[i][0] != c[i+1][0]:
        print 'equality failed for numbers: %d and %d' % (c[i][0], c[i+1][0])
    elif c[i+1][1] - c[i][1] > 3:
        print 'Subtraction is greater than three for: %d and %d' % (c[i][1], c[i+1][1])

print output

output:

equality failed for numbers: 1 and 4
equality failed for numbers: 4 and 5
[(1, 20150602), (1, 20150603), (4, 20150605), (4, 20150606)]

The reason you are missing two elements is because when i in the for loop is 2 c[i][0] will return 1. Now, when this section of the if statement is performed: c[i][0] == c[i+1][0] it returns false because c[i][0] returns 1 and c[i+1][0] returns 4 and they do not equal each other. The same happens when i is equal to 5.