barplot that displays sums of values of 2 y colums grouped by different variables

It is not generally advisable to get too fancy with stat functions in 
ggplot... things can easily get more complicated than ggplot is ready to 
handle when it comes to calculations. It is better to create data that 
corresponds directly to the graphical representations you are mapping 
them to.

Read [1] for more on this philosophy.

[1] H. Wickham, Tidy Data, Journal of Statistical Software, vol. 59, no. 
10, pp. 123, Sep. 2014. http://www.jstatsoft.org/v59/i10/

#---
library(ggplot2) # ggplot
library(dplyr)   # `%>%`, group_by, summarise
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#>     filter, lag
#> The following objects are masked from 'package:base':
#>
#>     intersect, setdiff, setequal, union
library(tidyr)   # gather

dta <- read.table( text =
"city n y
mon 100 200
tor 209 300
edm 98 87
mon 20 76
tor 50 96
edm 62 27
", header = TRUE )

dta2 <- (   dta
         %>% group_by( city )
         %>% summarise( n = sum( n )
                      , y = sum( y )
                      )
         %>% gather( Response, value, -city )
         )

ggplot( dta2, aes( x=city, y=value, fill = Response ) ) +
     geom_bar( stat="identity", position="dodge" )

#' ![](https://i.imgur.com/cosFf3B.png)
#---

I am trying to create a barplot displaying the sums of 2 columns of data 
grouped by a variable. the data is set up like this:

"city" "n" "y" <br>
mon 100 200 <br>
tor 209 300 <br>
edm 98 87 <br>
mon 20 76 <br>
tor 50 96 <br>
edm 62 27 <br>

the resulting plot should have city as the x-axis, 2 bars per city, 1 
representing the sum of "n" in that city, the other the sum of "y" in that 
city.

If possible also show the sum in each bar as a label?

I aggregated the data into sums like this:

sum_data <- aggregate(. ~ City,data=raw_data,sum)

this gave me the sums per city as I wanted but for some reason 1 of the 
cities is missing in the output.

Using this code for the plot:

ggplot(sum_data,aes(x = City,y = n)) + geom_bar(aes(fill = y),stat = 
"identity",position = "dodge")

gave be a bar plot with one bar per city showing the sum of y as a color 
gradient. not what I expected given the "dodge" command in geom_bar.

Thanks.

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