Find row with lowest value in COLUMNA, return row's COLUMNB

Question

I have a feeling this is one of those stupidly easy things where I'm just not using a function I should be.

Here's the relevant part of the function:

min(DATASET$COLUMNNAME, na.rm = TRUE)

Right now, it reports the correct value from COLUMNNAME--the lowest value in that column. Great. However, what I really want it to do is look across the dataframe to that result's entry in column NAME and print that. It should not print the minimum value at all, just the entry in NAME for the row with COLUMNAME's minimum value.

Is the best way to do it to get the row number of that minimum value somehow, and return DATASET$NAME[row,] ?

Answer 1

Looking for this maybe:

DATASET$NAME[DATASET$COLUMNNAME == min(DATASET$COLUMNNAME)]

That is, you select NAME from DATASET, where COLUMNAME has the minimum value.

If you don't like repeating DATASET so many times, this is equivalent using with:

with(DATASET, NAME[COLUMNNAME == min(COLUMNNAME)])

Answer 2

The function you are looking for is which.min:

> set.seed(123)
> df<-data.frame(name=sample(LETTERS[1:10]),value=sample(10))
> df
   name value
1     C    10
2     H     5
3     D     6
4     G     9
5     F     1
6     A     7
7     J     8
8     I     4
9     B     3
10    E     2
> df[which.min(df$value),]
  name value
5    F     1
> df$name[which.min(df$value)]
[1] F
Levels: A B C D E F G H I J