Chapter 7 Convert to a factor
pg\(treatment <- factor(pg\)treatment) pg #> weight group treatment #> 1 4.17 ctrl No #> 2 5.58 ctrl No #> 11 4.81 trt1 Yes #> 21 6.31 trt2 Yes #> 22 5.12 trt2 Yes
Here, we combined two of the factor levels and put the result into a new column. If you simply want to rename the levels of a factor, see Recipe \@ref(RECIPE-DATAPREP-FACTOR-RENAME).
The coding criteria can also be based on values in multiple columns, by using the `&` and `|` operators:
```r
pg$newcol[pg$group == "ctrl" & pg$weight < 5] <- "no_small"
pg$newcol[pg$group == "ctrl" & pg$weight >= 5] <- "no_large"
pg$newcol[pg$group == "trt1"] <- "yes"
pg$newcol[pg$group == "trt2"] <- "yes"
pg$newcol <- factor(pg$newcol)
pg
#> weight group newcol
#> 1 4.17 ctrl no_small
#> 2 5.58 ctrl no_large
#> 11 4.81 trt1 yes
#> 21 6.31 trt2 yes
#> 22 5.12 trt2 yesIt’s also possible to combine two columns into one using the interaction() function, which appends the values with a . in between. This combines the weight and group columns into a new column, weightgroup:
pg$weightgroup <- interaction(pg$weight, pg$group)
pg
#> weight group weightgroup
#> 1 4.17 ctrl 4.17.ctrl
#> 2 5.58 ctrl 5.58.ctrl
#> 11 4.81 trt1 4.81.trt1
#> 21 6.31 trt2 6.31.trt2
#> 22 5.12 trt2 5.12.trt2