r - Create a new column in dataframe by indexing into a list using another column? -

i have dataframe column of indices, , list maps each index value.

x <- data.frame( index = c("bob","tom","bob","harry") ) lst <- list( "bob" = 10, "tom" = 20, "harry" = 30 )

i create new column ("lookup") in dataframe using index column lookup appropriate value in list. thought ...

x$lookup <- lst[[ x$index ]] # nope, doesn't work

... might work, fails attempt of recursive indexing. following works, i'd avoid using loop if possible:

for (i in 1:nrow(x) ) { # works, ugly   x[ i, "lookup" ] <- lst[[ as.character( x[i,"index"] ) ]] }

yielding following desired result:

> x   index lookup 1   bob     10 2   tom     20 3   bob     10 4 harry     30

is there way accomplish without using loop?

i caught surprise creating 'x' generated dataframe column of factors rather strings. is using 'as.character' in loop best way index list?

new both r , stackoverflow, posting first question after unsuccessfully trying search answer. apologies newness.

you can try match

 x$lookup <- unlist(lst[match(x$index, names(lst))])  x  #  index lookup  #1   bob     10  #2   tom     20  #3   bob     10  #4 harry     30

or use stack/merge

  merge(x,stack(lst), by.x='index', by.y='ind')

JVParth