How to visualize two column in bar chart using R? - r

Question

I don't know if my question clear enough...
I have this table
Name Mark_Oral Mark_Written Total_M_Oral Total_M_Written
1 Hercule Poirot 50 49 858 781
2 Joe O'Neil 70 79 1056 1083
3 John McAuley 81 99 1219 1333
and I have to visualize the last two column in bar chart using R to compare student total mark
Data
table <- structure(list(Name = c("Hercule Poirot", "Joe O'Neil", "John McAuley"),
Mark_Oral = c(50L, 70L, 81L),
Mark_Written = c(49L, 79L, 99L),
Total_M_Oral = c(858L, 1056L, 1219L),
Total_M_Written = c(781L, 1083L, 1333L)),
.Names = c("Name", "Mark_Oral", "Mark_Written", "Total_M_Oral", "Total_M_Written"),
row.names = c("1", "2", "3"), class = "data.frame")

Answer 1

You can use + to combine other plots on the same ggplot object. For example:
ggplot(survey, aes(often_post,often_privacy)) +
geom_point() +
geom_smooth() +
geom_point(aes(frequent_read,often_privacy)) +
geom_smooth(aes(frequent_read,often_privacy))

Answer 2

With ggplot2 (as your tags suggest) the syntax is:
ggplot(data = table,aes(x= Total_M_Oral,y=Total_M_Written))+geom_bar(stat = "identity")
Where table is replaced by the name of your dataframe.
Edit
I was unsure that my first answer really answered your question (multiple uses of bars).
Create dummy data
df<-data.frame(x = rpois(n = 100,lambda = 800),y = rpois(n = 100,lambda = 800))
With previous plot:
If you want to count and have a color for Oral and one for written
df2<-data.frame(x = c(df$x,df$y),y = rep(c("written","oral"),each = nrow(df)))
ggplot(data = df2,aes(x= x,fill=y),alpha = I(0.5))+geom_bar(stat = "count")
Which gives:
Comment: alpha parameter is not necessary, it just deals with the transparency so that you can see when there are overlapping bars.
With student names
df3<-data.frame(name = rep(table$Name,times = 2),
y = c(table$Total_M_Oral, table$Total_M_Written),
fill = rep(c("oral","written"),each = nrow(table)))
ggplot(data = df3, aes(x = name,y= y,fill = fill,alpha = 0.5))+geom_bar(stat= "identity")