Legend showing stroke-only for alpha/transparency (geom_point)

torvaney · April 13, 2018, 12:53pm

Recently, I wanted to use two separate colour schemes on a chart, while keeping the information in the legend. In this case there was one colour scale for a set of points, and one for a set of lines.

I came up with a workaround whereby I mapped my chosen aesthetic to fill in the points instead, and used pch = 1 (circle with outline and fill) and stroke = 0. If this seems a bit confusing, refer to the reprex below.

However, another bit of data was mapped to the points' alpha (transparency)*. This leads to the points' alphs not being present in the legend (since the legend only shows the outline of the points, which is now stroke = 0).

library(ggplot2)

ggplot(mtcars, aes(x = disp, y = mpg)) +
  geom_point(aes(fill = vs, alpha = wt), 
             pch = 21,                        # Make points into filled points
             stroke = 0) +                    # Remove outline from filled points
  ggtitle("Alpha in legend with stroke = 0")

no_legend

I should also note that this is with ggplot2_2.2.1.9000 (via sessionInfo()).

My questions are:

Is this a bug? I.e. should I file an issue on github?
Is there a handier workaround to the initial issue?

* If you're thinking this is a sign there's too much going on in the chart, I would probably agree with you. Still, please bear with me.

mara · April 13, 2018, 1:38pm

For part one:

Yeah, legend problems are a known issue right now. I don't think you need to open a new issue, though, as I think this overlaps with existing open issues (see Upvoting issues post from yesterday ).

Take a look at (the link above is to all open issues re. legends right now):

github.com/tidyverse/ggplot2

The cross effect in legend when use geom_hline and geom_vline in the same plot.

opened 06:35PM - 15 Mar 18 UTC

closed 01:46PM - 27 Apr 18 UTC

fmassicano

That problem was very discussed in issue [geom\_vline messes up geom\_line legen…d, if show\_guide = TRUE](https://github.com/tidyverse/ggplot2/issues/1267), but a similar problem still happen, as was mentioned by [rdcominer](https://github.com/rdcomineor) in this [comment](https://github.com/tidyverse/ggplot2/issues/1267#issuecomment-187116698), when both hline and vline are in the same plot. _**The legend of that plot, regarding hline and vline will be overlapping.**_ Here's are the examples: ``` r library(ggplot2) df <- data.frame(x = c(1, 2), y = c(1, 2), z = c("a", "b")) threshold <- data.frame(x = c(1.2, 1.5), name = c("bar", "foo")) ``` Both legends are shown (vline and hline) which procude the cross effect ``` r ggplot(df, aes(x, y, colour = z)) + geom_point() + geom_vline(aes(xintercept = 1.25, linetype = "dotted"), colour= 'red', data = threshold) + geom_hline(aes(yintercept = 1.75, linetype = "1F"), colour= 'blue', data = threshold) + scale_linetype_manual(name = "Thresholds",values = c(2,2)) ``` ![unnamed-chunk-2-1](https://user-images.githubusercontent.com/1872321/37482519-5a458788-2852-11e8-8c1a-bfffb499fe13.png) I tried to use show.legend = FALSE in one of them, to see what happens, but ggplot2 preserve the pattern of another one in both legends. Then the next example, show us only geom\_vline legend which preserves the vline pattern in legends ``` r ggplot(df, aes(x, y, colour = z)) + geom_point() + geom_vline(aes(xintercept = 1.25, linetype = "dotted"), colour= 'red', data = threshold) + geom_hline(aes(yintercept = 1.75, linetype = "1F"), colour= 'blue', data = threshold, show.legend = FALSE) + scale_linetype_manual(name = "Thresholds",values = c(2,2)) ``` ![unnamed-chunk-3-1](https://user-images.githubusercontent.com/1872321/37482542-65e7c8ee-2852-11e8-9f49-d577df8a907b.png) The next one, the only geom\_hline legend is shown which preserve the hline pattern in legends ``` r ggplot(df, aes(x, y, colour = z)) + geom_point() + geom_vline(aes(xintercept = 1.25, linetype = "dotted"), colour= 'red', data = threshold,show.legend = FALSE) + geom_hline(aes(yintercept = 1.75, linetype = "1F"), colour= 'blue', data = threshold) + scale_linetype_manual(name = "Thresholds",values = c(2,2)) ``` ![unnamed-chunk-4-1](https://user-images.githubusercontent.com/1872321/37482548-6d7bfae4-2852-11e8-932d-b2f6d00f445a.png) ----- If is possible, would be nice to allow both hline and vline in the same plot, with a horizontal line in hline legend, and a vertical line in vline legend.

github.com/tidyverse/ggplot2

Error thrown for legend creation with multiple calls of geom_sf, when using show.legend

opened 05:47PM - 21 Feb 18 UTC

closed 11:54PM - 01 May 18 UTC

cseveren

bug layers

I am trying to graph several geographic datasets together using the `ggplot2` an…d the new (and awesome) simple features mapping packages `geom_sf`. I'm receiving an error when trying to get the legend to show up in a particular way, and `traceback()` indicates that the issues is due to `ggplot2`. Posts on both Stack Overflow and the `sf` git development site suggested I post here. Here is a minimum reproducible example, with the error `Error: length(rows) == 1 is not TRUE`. This example is due to user Gilles at Stack Overflow and replicates the issue I initially posted about (see links at bottom). library(sf) #> Linking to GEOS 3.5.1, GDAL 2.1.3, proj.4 4.9.2, lwgeom 2.3.2 r15302 library(ggplot2) # Create a ploygon object (with 3 polygons) poly1 <- cbind(lon=c(5, 6, 7, 5), lat=c(52, 53, 51, 52)) poly <- st_sf(st_sfc(list(st_polygon(list(poly1)), st_polygon(list(poly1 - 1)), st_polygon(list(poly1 + 1))))) poly$treatment <- factor(c("Omitted", "Control", "Treated")) # create two line objects line1 <- st_sf(st_sfc(list(st_linestring(cbind(lon = c(5.5, 4.5), lat = c(53.5, 54.5)))))) line2 <- st_sf(st_sfc(list(st_linestring(cbind(lon = c(5, 7.5), lat = c(53, 52)))))) ggplot() + geom_sf(data= line1, aes(color="A"), show.legend = "line") + geom_sf(data = poly, aes(fill = treatment)) #> Error: length(rows) == 1 is not TRUE Running `traceback()` indicates that the issues lies within `ggplot2`. If `show.legend` is omitted, no error is thrown, and a graph is created, but the legend is incorrect -- it is a box outlined in the correctly colored line, rather then just the line: ggplot() + geom_sf(data= line1, aes(color="A")) + geom_sf(data = poly, aes(fill = treatment)) ![mapwrong](https://user-images.githubusercontent.com/30906872/36496050-1eda4138-1705-11e8-9943-cf2f489c21e7.png) Links +[Stack Overflow Post](https://stackoverflow.com/questions/48873972/ggplot-and-geom-sf-and-error-lengthrows-1-is-not-true) +[sf git](https://github.com/r-spatial/sf/issues/643#issuecomment-367008590)

github.com/tidyverse/ggplot2

Allow multiple legends for same aesthetic but different layers

opened 07:09PM - 22 Mar 18 UTC

closed 03:56AM - 12 May 18 UTC

skanskan

feature scales

Imagine I want to plot this toy data: ``` lev <- c("A", "B", "C", "D") no…des <- data.frame(ord=c(1,1,1,2,2,3,3,4), brand= factor(c("A", "B", "C","B", "C","D", "B","D"), levels=lev), thick=c(16,9,9,16,4,1,4,1)) edge <- data.frame(ord1=c(1,1,2,3), brand1=factor(c("C","A","B","B"), levels=lev),ord2=c(2,2,3,4), brand2=c("C","B","B","D"), N1=c(2,1,2,1), N2=c(5,5,2,1)) ggplot() + geom_segment(data = edge, aes(x = ord1, y = brand1, xend = ord2, yend = brand2, size = N2/N1), color = "blue", show.legend = T) + geom_point(data = nodes, aes(x = ord, y = brand, size = thick), color = "black", shape = 16, show.legend = T) + scale_x_continuous(limits = c(1, 4), breaks = 0:4, minor_breaks = NULL) + scale_size_continuous(trans = "sqrt", breaks = c(1,4,9,16)) + ylim(lev) + theme_bw() ``` ![eusfg 1](https://user-images.githubusercontent.com/4120283/37792463-25697528-2e0c-11e8-9b1f-90e2adfe4369.png) I'm representing two variables two show sizes and I would like to get proper legends from them, but they overlap. I wrote this as a question at https://stackoverflow.com/questions/46695651/how-to-have-two-different-size-legends-in-one-ggplot but some people told me it's not possible to do it with ggplot, other only suggest alternatives. That's strange because you can do it even with base R plot. ![cghnh](https://user-images.githubusercontent.com/4120283/37792682-b6eb7bd6-2e0c-11e8-8697-c697fee32d78.png)

torvaney · April 13, 2018, 3:40pm

Thank you, Mara. I had a look at the issues on github, and as you suggest, I wasn't sure how much I'd contribute by adding a new one. It's good to get a more qualified confirmation.

Thank you for the link, I'll take a look and upvote any that seem applicable.

I'll be honest, since this is at best an edge case (and more reasonably, a hack), it seems like it'd be a very low priority fix anyway. It seems like a better general solution is to use

ggplot(data) +
  geom_point(aes(colour = var1, aes = var2), pch = 1) +
  ...