Apply function to dataframe with changing argument

Question

I have 2 objects:

A data frame with 3 variables:

v1 <- 1:10
v2 <- 11:20
v3 <- 21:30
df <- data.frame(v1,v2,v3)

A numeric vector with 3 elements:

nv <- c(6,11,28)

I would like to compare the first variable to the first number, the second variable to the second number and so on.

which(df$v1 > nv[1])
which(df$v2 > nv[2])
which(df$v3 > nv[3])

Of course in reality my data frame has a lot more variables so manually typing each variable is not an option.

I encounter these kinds of problems quite frequently. What kind of documentation would I need to read to be fluent in these matters?

Answer 1

One option would be to compare with equally sized elements. For this we can replicate the elements in 'nv' each by number of rows of 'df' (rep(nv, each=nrow(df))) and compare with df or use the col function that does similar output as rep.

 which(df > nv[col(df)], arr.ind=TRUE)

If you need a logical matrix that corresponds to comparison of each column with each element of 'nv'

 sweep(df, 2, nv, FUN='>')

Answer 2

You could also use mapply:

mapply(FUN=function(x, y)which(x > y), x=df, y=nv)
#$v1
#[1]  7  8  9 10
#
#$v2
#[1]  2  3  4  5  6  7  8  9 10
#
#$v3
#[1]  9 10