R/tidyverse: calculating standard deviation across rows

Question

Say I have the following data:

colA <- c(\"SampA\", \"SampB\", \"SampC\")
colB <- c(21, 20, 30)
colC <- c(15, 14, 12)
colD <- c(10, 22, 18)
df &l         


        

Answer 1

A different tidyverse approach could be:

df %>%
 rowid_to_column() %>%
 gather(var, val, -c(colA, rowid)) %>%
 group_by(rowid) %>%
 summarise(rsds = sd(val)) %>%
 left_join(df %>%
            rowid_to_column(), by = c("rowid" = "rowid")) %>%
 select(-rowid)

   rsds colA   colB  colC  colD
      
1  5.51 SampA    21    15    10
2  4.16 SampB    20    14    22
3  9.17 SampC    30    12    18

Here it, first, creates a row ID. Second, it performs a wide-to-long data transformation, excluding the "colA" and row ID. Third, it groups by row ID and calculates the standard deviation. Finally, it joins it with the original df on row ID.

Or alternatively, using rowwise() and do():

 df %>% 
 rowwise() %>%
 do(data.frame(., rsds = sd(unlist(.[2:length(.)]))))

  colA   colB  colC  colD  rsds
*     
1 SampA    21    15    10  5.51
2 SampB    20    14    22  4.16
3 SampC    30    12    18  9.17