Dynamically build call for lookup multiple columns

Question

How can I dynamically lookup multiple fields and add by reference using character vector variable as argument. In below case I want to lookup two columns and get ri

Answer 1

Here's the crude way:

myj <- parse(text=paste0("`:=`(",paste0(select,"=i.",select,collapse=","),")"))
ID[JN,eval(myj)]
#    id meta value
# 1:  1    1     x
# 2:  2    1     v
# 3:  3    1     f