Adding a column with relative frequencys to a r-dataframe

I have a dataframe in R and want to add a column with relative freuqencys to each variable.
Here is an example dataframe I am working with:

df <- data.frame(
  Ausprägung = c("Obs1", "Obs2", "Obs3", "Obs4", "Total"),
  Anzahl = c(100, 100, 100, 100, 400)
)

I want to add a column with the relative frequencys and have an output dataframe like the one shown down below

I tried working with the prop.table() function but got stuck because I want to work with a dataframe and the prop.table() functions only supports table-objects it seems. I found a few other questions about the calculation of relative frequencys but non of them seemed to fit my case.

>Solution :

This should work:

df <- data.frame(
  Ausprägung = c("Obs1", "Obs2", "Obs3", "Obs4", "Total"),
  Anzahl = c(100, 100, 100, 100, 400)
)

transform(df, rel.frequency = ifelse(Ausprägung == "Total", NA, Anzahl / sum(Anzahl[Ausprägung != "Total"])))
#>   Ausprägung Anzahl rel.frequency
#> 1       Obs1    100          0.25
#> 2       Obs2    100          0.25
#> 3       Obs3    100          0.25
#> 4       Obs4    100          0.25
#> 5      Total    400            NA

^{Created on 2023-11-09 with reprex v2.0.2}