library(dplyr)
## data
df =data.table::fread(
"
1 2 3
4 5 6
7 8 9
"
)
## tidyverse
df1 = df %>%
mutate(rowmax = pmax(V1,V2,V3))
df1
#> V1 V2 V3 rowmax
#> 1 1 2 3 3
#> 2 4 5 6 6
#> 3 7 8 9 9
## apply
df2 = df
df2$rowmax = apply(df,1, max)
df2
#> V1 V2 V3 rowmax
#> 1: 1 2 3 3
#> 2: 4 5 6 6
#> 3: 7 8 9 9
<sup>Created on 2019-02-03 by the reprex package (v0.2.1)</sup>