group by and scale/normalize a column in r

Question

I have a dataframe that looks like this:

  Store Temperature Unemployment Sum_Sales
1     1       42.31        8.106   1643691
2     1       38.51        8.106   1641957
3     1       39.93        8.106   1611968
4     1       46.63        8.106   1409728
5     1       46.50        8.106   1554807
6     1       57.79        8.106   1439542

What I can't figure out in R is how to group by and apply. So for each store (grouped), I want to normalize/scale two columns (sum_sales and temperature).

Desired output that I want is the following:

  Store Temperature Unemployment Sum_Sales
1     1       1.000        8.106   1.00000
2     1       0.000        8.106   0.94533
3     1       0.374        8.106   0.00000
4     2       0.012        8.106   0.00000
5     2       0.000        8.106   1.00000
6     2       1.000        8.106   0.20550

Here is the normalizing function that I created:

 normalit<-function(m){
   (m - min(m))/(max(m)-min(m))
 }

I'm using the dply package and can't seem to figure out how to group by and apply that function to a column. I tried something like this and get an error:

df2 <- df %.%
  group_by('Store') %.%
  summarise(Temperature = normalit(Temperature), Sum_Sales = normalit(Sum_Sales)))

Any suggestions/help would be greatly appreciated. Thanks.

Answer 1

The issue is that you are using the wrong dplyr verb. Summarize will create one result per group per variable. What you want is mutate. Mutate changes variables and returns a result of the same length as the original. See http://cran.rstudio.com/web/packages/dplyr/vignettes/dplyr.html. Below two approaches using dplyr:

df %>%
    group_by(Store) %>%
    mutate(Temperature = normalit(Temperature), Sum_Sales = normalit(Sum_Sales))

df %>%
    group_by(Store) %>%
    mutate_each(funs(normalit), Temperature, Sum_Sales)

Note: The Store variable is different between your data and desired result. I assumed that @jlhoward got the right data.