Question

This actually corresponds to my other question but things get more complicated. I have data.frame and vector:

df <- data.frame(key=c(0,3:6), value=c(0,52,26,12,1))
x <- c(3,4,3,3,5,5,6,6,6,6)

and need to obtain values from df based on x as keys:

[1] 52 26 52 52 12 12 1 1 1 1

Solution from previous answer can only give result with NO duplicates:

df[df$key %in% x,"value"]
[1] 52 26 12  1

Is there a way to solve this?

Also, I see hash() can do things like:

h <- hash( keys=letters, values=1:26 )
h$a # 1
h[ "a" ]
h[[ "a" ]]

z <- rep(letters[3:5],2)

h[z] # still with NO duplicates
<hash> containing 3 key-value pair(s).
c : 3
d : 4
e : 5

But seems like it cannot return a vector of values with something like:

h[[z]]
Error in h[[z]] : wrong arguments for subsetting an environment

Otherwise, it would be perfect so that we can get rid of data.frame by using some ‘real’ hash concept.

Thanks!

Answer 1

To answer your first question: Use match

df[match(x, df$key), ]

    key value
2     3    52
3     4    26
2.1   3    52
2.2   3    52
4     5    12
4.1   5    12
5     6     1
5.1   6     1
5.2   6     1
5.3   6     1

---

You should also have a look at Named vectors

dat <- c(0,52,26,12,1)
names(dat) <- as.character(c(0,3:6))

dat[as.character(x)]
 3  4  3  3  5  5  6  6  6  6 
52 26 52 52 12 12  1  1  1  1