从基于 R 中另一列中的条件的列中获取值？

Question

I have a data table like this:

DT <- data.table(score=c(78, 93, 88, 50), IQ=c(101, 95, 89, 90))

# DT output
score, IQ
78, 101
93, 95
88, 89
50, 90

I want to obtain the score at which IQ is the highest, eg here max(IQ)=101 so we would get 78.

Is there a way to do this by creating a new table and using:

new_DT <- DT[, list(scoreMaxIQ = ...)]

ie inside list(...) we create a new variable scoreMaxIQ for the score at which IQ is the highest?

Answer 1

You could do:

DT[,.(IQ, score,maxIQ = IQ[which.max(IQ)],scoreMaxIQ =score[which.max(IQ)] )]

    IQ score maxIQ scoreMaxIQ
1: 101    78   101         78
2:  95    93   101         78
3:  89    88   101         78
4:  90    50   101         78

Note the necessary conversion to numeric because "101"<"95" in character mode.