R Dplyr mutate, calculating standard deviation for each row

Question

I am trying to calculate the mean and standard deviation from certain columns in a data frame, and return those values to new columns in the data frame. I can get this to wo

Answer 1

You can also write your own vectorised RowSD function as in

RowSD <- function(x) {
  sqrt(rowSums((x - rowMeans(x))^2)/(dim(x)[2] - 1))
}

and then

mtcars %>% 
  mutate(mean = (hp + drat + wt)/3, stdev = RowSD(cbind(hp, drat, wt)))
##     mpg cyl  disp  hp drat    wt  qsec vs am gear carb      mean     stdev
## 1  21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4  38.84000  61.62969
## 2  21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4  38.92500  61.55489
## 3  22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1  33.05667  51.91809
## 4  21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1  38.76500  61.69136
## 5  18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2  60.53000  99.13403
## 6  18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1  37.07333  58.82726
## ...