R：如何根据列条件和另一个df的百分比值执行（用户定义的）计算？

Question

I want to calculate the percentage values for a data.frame column based on criterion of another object's column using percentages of another df. Here is some example data:

   df <- data.frame(Value = c(50,10,30,40),
                    object = c("apples","tomatoes", "apples","pears" ))

and a share object with the percentages for the objects:

share <- data.frame(object = c("tomatoes","pears", "apples" ),
                   percentage = c(90,75,80))

My expected result is:

  Value   object
1    40   apples
2     9 tomatoes
3    24   apples
4    30    pears

With only one object I used this code, which works fine:

df[,1] <- df$Value * share$percentage /100 

But how to perform this for the different objects in df/share? "aggregation"/"subset" or something like that?

EDIT: I have tried this so far, which I think it could be a way:

df[,1] <- aggregate(df$Value, by=df$object,FUN= function(x) {x$Value * share$percentage /100}   )

and

df[,1] <- apply(split(df, df$object) function(x) {x$Value * share$percentage / 100})

However, the function seems to be wrong (I'm nor really familar with functions:). Please note, that I don't want first to merge df with share as answered, as I need the original structure of df and order. So I'm looking for a short command. I really appreciate your ideas. Thanks

Answer 1

Do you want a weighted average?

library(dplyr)

df %>%
  inner_join(share) %>%
  group_by(object) %>%
  summarize(weighted_average = 
              sum(Value * percentage) / sum(percentage) )