如果在使用lambda，map和list时Boolean为True，如何返回以下位置的列表？

Question

I have a list of names and after each name is a number. Like this

l = ["Bob", 4, "Rob", 5, "Sam", 6, "Bob", 5]

I would like to return a list of numbers that correspond to a given name, by only using lambda, map, list or filter.

For example, if I were to use the name Bob with list = ["Bob",4,"Rob",5,"Sam",6,"Bob",5] , my output would be

[4,5]

I think I understand most of lambda, I just can't get it to return what I want it too.

mx = list(map(lambda x: l[x+1] if x == name, l))

I am getting this error. Syntax Error: invalid syntax: <string>, line 14, pos 29

Answer 1

You can run through values at even indexes and output the value at the next index when it matches the name:

result = [l[i+1] for i in range(0,len(l),2) if l[i] == "Bob"]

If you're allowed to use enumerate, this can be a bit more concise (assuming none of the odd indexes contain a matching string):

result = [l[i+1] for i,n in enumerate(l) if n == 'Bob' ]

or using zip()

result = [v for n,v in zip(l,l[1:]) if n == 'Bob']

Answer 2

Reconstruct the list into a list of tuples; then a list comprehension is trivial:

items = [number for (name, number) in zip(l[0::2], l[1::2]) if name == "Bob"]