Understanding dates a plotting with ggplot2 in R

Question

I have a CSV file called gdata.csv, with data like:

id,date,totKm,eLiter,euros,liters,km
1,24-04-2010,23678,1.180,42.00,35.59,450
2,16-05-2010,24058,1.200,43.00,35.83,380
3,27-05-2010,24488,1.160,44.00,37.93,430
4,12-06-2010,24960,1.180,45.00,38.14,472

With ggplot2

I just want to plot date and eliter in a line char with ggplot2, with this code:

x_date <- as.Date(gdata$date, format = "%d-%m-%Y")
ggplot(eliter, aes(x_date, eliter)) + geom_line()

But, it returns this error related with the class: Error: ggplot2 doesn't know how to deal with data of class numeric

I have tried to make a data.frame but it stills returns the error:

d <- data.frame(xdate = x_date, yeliter=gdata$eLiter)
ggplot(d$xdate, aes(d$xdate, d$yeliter)) + geom_line()

Error: ggplot2 doesn't know how to deal with data of class Date

With plot

I have managed to do this with plot() function:

plot(gdata$eLiter~as.Date(gdata$date, "%d-%m-%Y"), type = "s", xlab="Date",ylab="€/Liter", main="€/liter trend", col='blue')

And it works fine! But I can not do it with ggplot.

Could anyone help me?

Thank you very much.

After adding x_date to your data frame, still pass ggplot the entire data frame, that is ggplot(d, aes(...)) not ggplot(d$xdate, aes(...)). The error message is telling you that you're passing ggplot a single vector of dates where it's expecting a full data frame. — Gregor Thomas
– Gregor Thomas, Commented Aug 28, 2015 at 18:12
Also, don't use $ inside aes(). The point of ggplot having a data argument is that you don't keep re-typing the data frame. ggplot(d, aes(x = xdate, y = yeliter)) + geom_line(). — Gregor Thomas
– Gregor Thomas, Commented Aug 28, 2015 at 18:14

G. Grothendieck · Accepted Answer · 2015-08-28 19:53:42Z

1

Add + scale_x_date() like this:

Lines <- "id,date,totKm,eLiter,euros,liters,km
1,24-04-2010,23678,1.180,42.00,35.59,450
2,16-05-2010,24058,1.200,43.00,35.83,380
3,27-05-2010,24488,1.160,44.00,37.93,430
4,12-06-2010,24960,1.180,45.00,38.14,472"

DF <- read.csv(text = Lines)
DF$date <- as.Date(DF$date, "%d-%m-%Y")

library(ggplot2)
ggplot(DF, aes(date, eLiter)) +
  geom_line() +
  scale_x_date()

answered Aug 28, 2015 at 19:53

G. Grothendieck

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