new column mutate by group summary

[PeterHui]

Hi,

Does anyone know do a summary by group? I have the below dataframe and it comes with totals already.

I want to create a new column, using mutate, that will sum those trees together. Like this image below.

I tried ungroup() and doing another mutate but it doesn't seem to work. I've found a work around by creating a new summary by Counties only and doing a simple join but it has to be easier.

Trees = data.frame(
  stringsAsFactors = FALSE,
      Trees_COUNTY = c("Thunder Bay","Thunder Bay",
                       "Thunder Bay","Frontenac","Frontenac","Frontenac",
                       "Durham","Durham","Durham"),
            Stores = c("A", "B", "C", "A", "B", "C", "A", "B", "C"),
             Trees = c(761L, 1581L, 17201L, 351L, 421L, 15771L, 1891L, 291L, 14211L)
)
```r

[nirgrahamuk]

group_by(Trees,
         Trees_COUNTY) %>% mutate(
           sum_at_county_level = sum(Trees)
         )

[PeterHui]

Thanks for the quick reply, it's even faster than my edit to the post. I'll give it a try.

Works great thanks!