Question

For example, how do I get a vector of each and every person’s age in the list people below:

> people = vector("list", 5)
> people[[1]] = c(name="Paul", age=23)
> people[[2]] = c(name="Peter", age=35)
> people[[3]] = c(name="Sam", age=20)
> people[[4]] = c(name="Lyle", age=31)
> people[[5]] = c(name="Fred", age=26)
> ages = ???
> ages
[1] 23 35 20 31 26

Is there an equivalent of a Python list comprehension or something to the same effect?

Answer 1

You can use sapply:

> sapply(people, function(x){as.numeric(x[2])})
[1] 23 35 20 31 26