Barplot of summed values per category in R - currently plotting highest value only

Question

I have a data set (named data) as follows

  site  year  month  supplier   FG   total  
540853  2015      1    790122  T25       3  
540853  2015      3    790122  T25       5  
540853  2015      3    790122  V24       8  
540853  2015      4    790122  V24       1  
540853  2015      4    790122  T25       6  
540853  2015      4    790122  W29       4  
540853  2015      5    790122  W29       9  
540853  2015      5    790122  V24       2  
540853  2015      5    790122  T25       7 

I would like to create a bar plot for all the months ins 2015, suppler 790122, showing the sum of totals for each FG. The x-axis would have T25, W29 and V24. The y-axis would read 23 for T25 (3+5+8+7), 13 for W29 (4+9) and 11 for V24 (8+1+2).

I initially plotted using the following code

plot1 <- ggplot(subset(data, Year %in% c("2015") & supplier %in% c("520302")), 
                aes(x = factor(FG), y = total)) + 
         geom_bar(stat = "identity", position = "dodge") +
         theme(panel.grid = element_blank(), panel.background = element_blank(), axis.line = element_line(colour = "black"))

This produced a barplot that I thought was correct. However, I later wanted to add a table beside it so the readers could see the exact values for each FG, rather than reading it from the graph. Upon doing this I realised that the values in the barplot did not match the values in the table.

I plotted a second graph with the following code

for (i in 790122){
  For_summary <- subset(data, year %in% c("2015") & supplier %in% i)
  summary_tbl <- data.frame(ddply(For_summary, c("FG"), summarise, S = sum(total)))
  colnames(summary_tbl) <- c("FG", "total")
}

plot2 <- ggplot(summary_tbl, 
                aes(x = factor(FG), y = total)) + 
  geom_bar(stat = "identity", position = "dodge") +
  ylim(0,25) + labs(title = "plot 2") +
  theme(panel.grid = element_blank(), panel.background = element_blank(), axis.line = element_line(colour = "black"))

This gave a barplot with the values I want (see attached image). In the first barplot the R code seems to plot only the highest value for each of the FG.

Can anyone advise on what part of the code is doing this and how I can plot it correctly without having the create the summary_tbl in the for loop first?

Answer 1

Try aggregating the data first:

df2 <- aggregate(total~FG, df, sum)

ggplot(df2, aes(FG, total)) + 
  geom_bar(stat="identity")

Or as mentioned in the comments, it is possible to summarize in the function:

ggplot(df, aes(FG, total)) +
  geom_bar(stat="summary", fun.y="sum")

A third option is to remove the "position=dodge" argument of your original data. Use that parameter for grouped bar graphs.