How to compare two lists of same length (but different data types) and their corresponding values?-CodePudding

I have two lists...

depth = [1, 2, 3, 2, 1]
direction = ['x', 'y', 'z', 'x', 'x']

I want to compare the two of these lists and for each instance of direction == 'x', continually add the corresponding values in depth together. So I should get a value of 4 since 1 2 1 = 4 and it corresponds to each 'x' string in list direction.

The lists depth and direction are greatly abbreviated for example purposes. I want to iterate over both lists and in reality they contain a couple thousand values each.

I have already created a zip() and tried working with it like this:

dndzip = zip(depth, direction)
x = 0
for i,j in dndzip:
    if i == 'x':
        x  = j
return x

print(x)

I actually had this for loop under a defined function, but unfortunately this for loop doesn't return the proper value. I get a value and no errors, but it's always a value of 2 and not sure where I'm going wrong here.

CodePudding user response：

You can use dict.setdefault to add each direction's corresponding depth iteratively:

d = {}
for i,j in zip(direction, depth):
    d.setdefault(i, 0)
    d[i]  = j
out = list(d.items())

Alternatively you can use collections.defaultdict:

from collections import defaultdict
d = defaultdict(int)
for i,j in zip(direction, depth):
    d[i]  = j
out = list(d.items())

Output:

[('x', 4), ('y', 2), ('z', 3)]

CodePudding user response：

I'm not sure why you're getting 2 exactly, as when I ran the above code I got 0. But the reason for that is because in your loop, when you're decompressing your list with

dndzip = zip(depth, direction)
for i,j in dndzip:

notice that you zipped your list with depth as the first argument, so in this case i is depth and j is direction, so x =j is never run because i (depth) is never 'x'. To fix this, you would do:

dndzip = zip(depth, direction)
x = 0
for j,i in dndzip:
    if i == 'x':
        x  = j

print(x)

CodePudding user response：

In your particular code, it looks like you have the i and j mixed up. When you do dndzip = zip(depth, direction), dndzip is going to contain tuples where the first item is the item from depth, and the second is the one from direction. Meaning that something like

def sum_x_depths(depth, direction):
    dndzip = zip(depth, direction)
    x = 0
    for i,j in dndzip:
        if i == 'x':
            x  = j
    return x

will fail, since things like if i == 'x': are comparing i, which is an int, to 'x' which is a str. Then x = i also fails, because j is a str and x is an int. Make sure to try and make variable names refer to what they represent!

def sum_x_depths(depths, directions):
    s = 0
    for depth, direction in zip(depths, directions):
        if direction == 'x':
            s  = depth
    return s

You can also use the sum function and generator comprehensions to nice effect here, though it might be a bit long on a single line with these names:

def sum_x_depths(depths, directions):
    return sum(depth for depth, direction in zip(depths, directions) if direction == 'x')