# R – Calculate means including all factor levels but one

lets say, we use the dataframe mtcars and I would like to add the column qsec_control which is calculated as the mean(qsec) of all rows that don’t have the same cyl as the current row (e.g. if cyl == 6, it would take mean(qsec[cyl != 6]) ).
The question feels somewhat dumb, but I cant figure out how to do this.

### >Solution :

This solution groups by `cyl`, then uses `dplyr::cur_group_rows()` to index into `mtcars\$qsec`:

``````library(dplyr)

mtcars %>%
group_by(cyl) %>%
mutate(
qsec_control = mean(mtcars\$qsec[-cur_group_rows()])
) %>%
ungroup()
``````
``````# A tibble: 32 × 12
mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb qsec_cont…¹
<dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>       <dbl>
1  21       6  160    110  3.9   2.62  16.5     0     1     4     4        17.8
2  21       6  160    110  3.9   2.88  17.0     0     1     4     4        17.8
3  22.8     4  108     93  3.85  2.32  18.6     1     1     4     1        17.2
4  21.4     6  258    110  3.08  3.22  19.4     1     0     3     1        17.8
5  18.7     8  360    175  3.15  3.44  17.0     0     0     3     2        18.7
6  18.1     6  225    105  2.76  3.46  20.2     1     0     3     1        17.8
7  14.3     8  360    245  3.21  3.57  15.8     0     0     3     4        18.7
8  24.4     4  147.    62  3.69  3.19  20       1     0     4     2        17.2
9  22.8     4  141.    95  3.92  3.15  22.9     1     0     4     2        17.2
10  19.2     6  168.   123  3.92  3.44  18.3     1     0     4     4        17.8
# … with 22 more rows, and abbreviated variable name ¹​qsec_control
``````