R subscript based on a vector

Question

df <- data.frame(name=c('aa', 'bb', 'cc','dd'), 
              code=seq(1:4), value= seq(100, 400, by=100))
df

v <- c(1, 2, 2)
v

A <- df[df$code %in% v,]$value
A

str(A)

I tried to obtain the corresponding value based on the code. I was expecting A to be of length 3; but it actually returns a vector of 2. What can I do if I want A to be a vector of 3, that is c(100,200,200)?

Answer 1

%in% returns a logical vector, the same length as vector 1, that indicates whether each element of vector 1 occurs in vector 2.

In contrast, the match function returns, for each element of vector 1, the position in vector 2 where the element first appears (or NA if it doesn't exist in vector 2). Try the following:

df[match(v, df$code), 'value']

Answer 2

You could just use v as an argument if those were the lines whose "value"s you wanted:

> df[v,]$value
[1] 100 200 200

Answer 3

df[v,2] # minimum characters :)