CODEWITHSUNDEEP
rggplot2histogramsmoothingdensity-plot
Moritz Schmid
Moritz Schmid

Reputation: 395

Need smoothed line on histogram. Why does geom_density draw two lines?

I have an issue with my histogram on top of which I want to add a smoothed line, preferably a polynomial smooth.

The closest I got was adding a smoothed geom_density, or geom_line with stat="density" with additional adjust option.

In any case, I am getting two lines for my density, also when using the simplified code below. Why is that? I only want one smoothed density line or polynomial smooth.

Example data can be found here: https://www.dropbox.com/s/13795hnpqmwftnq/chyp3histo_total_lip.rda?dl=0

Using this code:

histos1a<-ggplot(data=chyp3histo_total_lip,aes(x=totallipid))+
 geom_histogram(color=col,fill=col)+
 geom_histogram(fill="white")+ 
 geom_density()

Gives: enter image description here

Why does it draw the two lines which seem like a range?

Cheers and thanks!

Upvotes: 1

Views: 3215

Answers (1)

Ben Bolker
Ben Bolker

Reputation: 226532

The problem is that you have a grouped tibble; apparently (to my surprise) ggplot2 pays attention to this. Try 

cc <- dplyr::ungroup(chyp3histo_total_lip)
ggplot(data=cc,...) ## etc.

If you had posted the results of str(chyp3histo_total_lip) we would have been able to diagnose this without downloading the data ...

str(chyp3histo_total_lip)
Classes ‘grouped_df’, ‘tbl_df’, ‘tbl’ and 'data.frame': 544 obs. of  1 variable:
 $ totallipid: num  NA 0.046 NA NA NA ...
 - attr(*, "vars")= chr  "haul" "pred"
 - attr(*, "drop")= logi TRUE
 - attr(*, "indices")=List of 2
  ..$ : int  0 1 2 3 4 5 6 7 8 9 ...
  ..$ : int  122 123 124 125 126 127 128 129 130 131 ...
 - attr(*, "group_sizes")= int  244 300
 - attr(*, "biggest_group_size")= int 300
 - attr(*, "labels")='data.frame':  2 obs. of  2 variables:
  ..$ haul: Factor w/ 2 levels "17:47h","1:44h": 1 2
  ..$ pred: Factor w/ 12 levels "C. glacialis C3",..: 5 5
  ..- attr(*, "vars")= chr  "haul" "pred"
  ..- attr(*, "drop")= logi TRUE

Upvotes: 3

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