使用ggplot2在barplot中显示多个数字列？

Question

Would anybody please help using ggplot2 in R, to show a barplot, where i need to show columns (first, second, third, fourth, fifth) on x axis and their values on y-axis ? without showing the column "uname".

    > head(golQ1Grades)
               qname          uname first second third fourth fifth 
1 onlinelernen_quiz_1          xxx   100      0     0      0     0      
2 onlinelernen_quiz_2        xxxx    100      0     0      0     0      
3 onlinelernen_quiz_4        xxxx     42     71     0      0     0       
4 onlinelernen_quiz_7        xxxx     85    100     0      0     0      
5 onlinelernen_quiz_1        xxx      85    100     0      0     0      
6 onlinelernen_quiz_3         xxxx    71      0     0      0     0       

Thanks for the advanced help.

Answer 1

It is my guess that you would like to display the mean value on the Y-axis.

library(ggplot2)

Data

dat<-data.frame(c(100,100,42,85,85,71), c(0,0,71,100,100,0), c(0,0,0,0,0,0), c(0,0,0,0,0,0), c(0,0,0,0,0,0))
names(dat)<-NULL

Compute mean and get new data

v1<-apply(dat, 2, mean)
nv1<-c("first","second","third", "fourth","fifth")
ndat<-data.frame(nv1, v1)

Plot

p <- ggplot(ndat, aes(factor(nv1), v1)) 
p + geom_bar(stat="identity")

Answer 2

I think the better option is dplyr and tidyr .Eg (I change data.frame a little)

library(dplyr)
library(tidyr)
library(ggplot2)

df  <- data.frame(qname = letters[1:10],
                          first = seq(1,10,1), 
                          second = seq(10,100,10),
                          third = seq(2,20,2))

And then use gather feature:

df <- df %>%
  gather(variable, value, -qname)

in your case it will be

df <- golQ1Grades %>%
  gather(variable,value, -qname, -uname)

Futhermore, instead of computing average value it is also extremely helpful facet_grid :

ggplot(df, aes(factor(qname),value))+
  geom_bar(stat = "identity")+
  facet_grid(.~variable)