How do I add a straight line to a qq plot?


#1

I’ve created a set of values using a gamma distribution and I’m trying to plot a qq plot for the data. I would like to have a straight line against the qq plot for comparison but can’t figure out how to add this to the qq plot. This is the code I am using at the moment:

Z <- rgamma(1000, shape = 0.1, scale = 10)
params <- as.list(fitdistr(Z, “gamma”)$estimate)

qplot(sample = Z, geom = ‘blank’) +
stat_qq(distribution = qgamma, dparams = params)


#2

you can use stat_qq_line() like this:

library(tidyverse)


Z <- rgamma(1000, shape = 0.1, scale = 10) 
params <- as.list(MASS::fitdistr(Z, "gamma")$estimate)

qplot(sample = Z, geom = "blank") +
  stat_qq(distribution = qgamma, dparams = params) +
  stat_qq_line(distribution = qgamma, dparams = params)

#3

Hi, I tried running your code but get the following error after the second line:
In densfun(x, parm[1], parm[2], …) : NaNs produced

and this error after the last line:
Error in match(x, table, nomatch = 0L) :
‘match’ requires vector arguments


#4

Are you trying to use the fitdistr function from the MASS package? I assumed you were. The code runs on my machine. Can you provide a reprex of the code that generated the error?


#5

Hi, when I try to install the development version it fails to install, something to do with R being confused by E:/UNI PROGRAMS and not understanding the space? It’s just the name of a folder but it looks like it loses the PROGRAMS part?

And then when using reprex() I highlighted and copied the relevant code but reprex() said no input and no access to clipboard.
I took a picture here as I can’t really think of a better way to show you sorry.
https://i.imgur.com/8yNRW0n.png

The part of your code I am running looks like this with error messages shown at the bottom.
https://i.imgur.com/JosDwNL.png

I should say that in order for qplot() to work I had to install qqplotr as you can see as it didn’t find it just from using library(tidyverse)

Sorry this is all a bit of a mess but I’m not sure what the issue with reprex is.


#6

The current version of reprex on CRAN has some issues.

Until CRAN catches up with the latest version install reprex with

devtools::install_github(“tidyverse/reprex”)