ggplot not graphing in

Question

I've been looking at this for a while now, does anyone see anything wrong with this ggplot syntax? I am getting this error:

Error: Discrete value supplied to continuous scale

this is z:

     Month Value
1  2011-01-01    11
2  2011-02-01     5
3  2011-03-01     6
4  2011-04-01     6
5  2011-05-01     4
6  2011-06-01     5
7  2011-07-01     3
8  2011-08-01     9
9  2011-09-01    19
10 2011-10-01     3
11 2011-11-01     6
12 2011-12-01     2
13 2012-01-01     1
14 2012-02-01     4
15 2012-04-01     1
16 2012-05-01     2
17 2012-06-01    11
18 2012-07-01     5


ggplot(z, aes(Month, Value)) + 
  geom_bar(fill="orange",size=.3)  + 
  theme_bw() + scale_x_discrete(name="Date") +   
  scale_y_continuous("Number") +
  opts(title="Monthly issues", 
       axis.title.x = theme_text(face="bold", colour="#990000"), 
       axis.text.x  = theme_text(angle=90), 
       axis.title.y = theme_text(face="bold", colour="#990000", angle=90)
   ) + 
  geom_smooth(data=z,aes(Month,Value,group=1), method="lm", size=2, color="darkblue")

It runs fine for me and produces a plot just fine. Check str(z) and make sure that you don't have Value stored as a factor. — joran
– joran, Commented Jul 19, 2012 at 14:32
this is the output of str(z): str(z) 'data.frame': 18 obs. of 2 variables: $ Month: Date, format: "2011-01-01" "2011-02-01" "2011-03-01" "2011-04-01" ... $ Value: num 11 5 6 6 4 5 3 9 19 3 ... — Mike Dude
– Mike Dude, Commented Jul 19, 2012 at 14:33

joran · Accepted Answer · 2012-07-19 14:40:31Z

5

Aha! The problem is your Month column, which as you note in your comment is stored as a Date. R considers this a continuous variable, hence the error with scale_x_discrete. You should probably convert it to a character with as.character if you want to use it with geom_bar.

answered Jul 19, 2012 at 14:40

joran

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3 Comments

Mike Dude Over a year ago

yes when I did this z$Month<-as.Character(z$Month), I can manually run and I see the graph. Problem is that when I try to run this line of code in an R script, my images are not populated: png(paste(m,"-","Issues",".png",sep=""), height=700, width=650) and that ggplot command and dev.off(), png files are created but they are empty.

joran Over a year ago

@MikeDude That's an entirely different problem that is so common it is a FAQ.

Mike Dude Over a year ago

thank you so much. That was a great catch (as.character). I was finally able to get around the image generation by grid.arrange, not sure better ways but, this will do it for me.

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