Compute the mean of two columns in a dataframe

We can use rowMeans

 a$mean <- rowMeans(a[,c('high', 'low')], na.rm=TRUE)

NOTE: If there are NA values, it is better to use rowMeans

For example

 a <- data.frame(High= c(NA, 3, 2), low= c(3, NA, 0))
 rowMeans(a, na.rm=TRUE)    
 #[1] 3 3 1

and using +

 a1 <- replace(a, is.na(a), 0)
 (a1[1] + a1[2])/2
#  High
#1  1.5
#2  1.5
#3  1.0

NOTE: This is no way trying to tarnish the other answer. It works in most cases and is fast as well.

For the mean of two numbers you don't really need any special functions:

a$mean = (a$high + a$low) / 2

For such an easy case, this avoids any conversions to matrix to use apply or rowMeans.

Related