How do I obtain values from a graphic?

Question

I did a distribution fit and was taking a look at the Q-Q-Plot and was wondering if there is an easy way to get the corresponding values from the graphic.

library("fitdistrplus")
data <- c(1050000, 1100000, 1230000, 1300000, 1450000, 1459785, 1654000, 1888000)
lognormalfit <- fitdist(data, "lnorm")
qqcomp(lognormalfit)

With the last line of code I receive the Q-Q-Plot without calculating the values. But I am also interested in the values. How can I obtain them?

Best regards Norbi

Answer 1

qqcomp has an option to produce the plot using ggplot2: this type of plot returns an object with the data. So you can grab the plot and data with

plotData <- qqcomp(lognormalfit, plotstyle = "ggplot") 

and then you can grab the relevant data from the plot object using

plotData$data
#   values   ind   sdata
#1 1026674 lnorm 1050000
#2 1158492 lnorm 1100000
#3 1247944 lnorm 1230000
#4 1327616 lnorm 1300000
#5 1407939 lnorm 1450000
#6 1497825 lnorm 1459785
#7 1613479 lnorm 1654000
#8 1820639 lnorm 1888000

Answer 2

To elaborate a little on my comment above, you can edit a function within R like this:

qqcompValues <- edit(qqcomp)

Within the editor, replace line 111 with the following:

return(data.frame(x=fittedquant, y=sdata))

Note, that the above edit assumes you are using the default plotstyle="graphics" function parameter.

You can then get QQ values like this:

qqValues <- qqcompValues(lognormalfit)
qqValues
        x       y
1 1026674 1050000
2 1158492 1100000
3 1247944 1230000
4 1327616 1300000
5 1407939 1450000
6 1497825 1459785
7 1613479 1654000
8 1820639 1888000