R thinks columnwise, not rowwise, at least in standard dataframe operations. A typical *rowwise* operation is to compute row means or row sums, for example to compute person sum scores for psychometric analyses.

One workaround, typical for R, is to use functions such as `apply`

(and friends).

However, `dplyr`

offers some quite nice alternative:

```
library(dplyr)
mtcars %>%
rowwise() %>%
mutate(mymean=mean(c(cyl,mpg))) %>%
select(cyl, mpg, mymean)
```

```
## Source: local data frame [32 x 3]
## Groups: <by row>
##
## # A tibble: 32 × 3
## cyl mpg mymean
## <dbl> <dbl> <dbl>
## 1 6 21.0 13.50
## 2 6 21.0 13.50
## 3 4 22.8 13.40
## 4 6 21.4 13.70
## 5 8 18.7 13.35
## 6 6 18.1 12.05
## 7 8 14.3 11.15
## 8 4 24.4 14.20
## 9 4 22.8 13.40
## 10 6 19.2 12.60
## # ... with 22 more rows
```