Hello,

I am struggling with the mutate function of dplyr package. Basically, I want to compute the errors made in a specific task.

```
mydata2 <- mutate(mydata2, error_letter = if_else ((letter == "A")) & ((key_DT_resp1.keys == "z" |key_DT_resp2.keys == "z")),0,1,
((letter == "E")) & ((key_DT_resp1.keys == "x" |key_DT_resp2.keys == "x")),0,1,
((letter == "U")) & ((key_DT_resp1.keys == "c" |key_DT_resp2.keys == "c")),0,1)
```

The error message I receive is:

`Problem with `mutate()` input `error_letter`. x Argument "true" fehlt (ohne Standardwert) i Input `error_letter` is `&...`.`

Alternatively, I tried:

```
mydata2 <- mutate(mydata2, error_letter = case_when((letter == "A")) & key_DT_resp1.keys == "z" |key_DT_resp2.keys == "z"~0,
((letter == "E")) & key_DT_resp1.keys == "x" |key_DT_resp2.keys == "x"~0,
((letter == "U")) & key_DT_resp1.keys == "c" |key_DT_resp2.keys == "c"~0)
```

Receiving:

```
x Input `error_letter` must be a vector, not a `formula` object.
```

How can I solve this issue? Any help would be appreciated.

thx in advance.