Creating a reactive rectangular plot

Question

I am relatively new to R. I am making an R Shiny app, and based on the input of the user, I would like to analyze the data and output a bar that shows the Jaccard index. This is what I want it to look like, although obviously a smooth gradient:

Please note that the Jaccard index (in this case, 0.35) will change after each input, so I'd like something reactive. I just have no idea where to start or if making plots like this is even possible in R.

Thanks.

edit: I used an online gradient generator to come up with this plot instead: how could I overlay a vertical line with its corresponding Jaccard index and corresponding location on the bar on this particular image?

edit: I want to remove the white space before the actual plot and after my text. any ideas?

score 1 · Accepted Answer · answered Sep 06 '17 at 06:27

1

With the plotrix package:

library(plotrix)
# get an empty box
plot(0:10, type="n", axes=FALSE, xlab=NA, ylab=NA)
# rectangle filled with a gradient
gradient.rect(0, 0, 10, 5, col=smoothColors("red",38,"blue"), border=NA)
# vertical bar 
segments(3.5, 0, 3.5, 5, lwd=2)
text(3.5, 0, "0.35", pos=1, xpd=TRUE)

answered Sep 06 '17 at 06:27

Stéphane Laurent

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how do I use this in R Shiny? how can I simply `return` one object, aka this plot, in a `reactive` function? in your code, each line builds upon each other, so I don't know what to do... – sweetmusicality Sep 06 '17 at 19:18
1

@sweetmusicality in `renderPlot`, you don't have to return "one object" – Stéphane Laurent Sep 06 '17 at 19:30
don't you have to only return one object though? – sweetmusicality Sep 06 '17 at 19:31
nvm, it works - thanks a bunch! quick question - how do I remove all the excess white space around the plot? I have updated my question to show you what I mean – sweetmusicality Sep 06 '17 at 21:42
@sweetmusicality Start with `plot(0, 0, xlim=c(0,10), ylim=c(0,5))` and adapt `xlim` and `ylim` if needed. – Stéphane Laurent Sep 07 '17 at 07:24

Ameya · Answer 2 · 2017-09-06T21:49:34.747

1

For something in base R, an imperfectly modified version of this solution, might work.

color.bar <- function(lut, min, max=-min, nticks=11, ticks=seq(min, max, len=nticks), title='') {
  scale = (length(lut)-1)/(max-min)
  dev.new(width=1.75, height=5)
  plot(c(min,max), c(0,10), type='n', bty='n', xaxt='n', xlab='', yaxt='n', ylab='', main=title)
  for (i in 1:(length(lut)-3)) {
    x = (i-1)/scale + min
    rect(x, 0 ,1, 30/scale, col=lut[i], border=NA)
  }
}

Then make the graph as follows -

color.bar(colorRampPalette(c("light green", "yellow", "orange", "red"))(100), 0, 1)

At this point perhaps you can add an abline(v = 0.35) to get what you want? You could even try pointing to the appropriate position using an arrow using

arrows(0.35, -1, 0.35, 0, length = 0.07, angle = 25)

edited Sep 06 '17 at 21:49

answered Sep 06 '17 at 06:41

Ameya

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where do I specify for it to be "0.35" of the way in? bc right now your "0.35" is almost "0.66" and I tried other values in your code in your arrows function, and couldn't figure out where to change it – sweetmusicality Sep 06 '17 at 18:56
thanks :) one last question - how do I add the value underneath, or at least near, the arrow? – sweetmusicality Sep 06 '17 at 21:54
try `text(0.35, 0.1, labels = '0.35', cex = 0.8)` – Ameya Sep 06 '17 at 22:39
thanks! how can I remove the white space from the image (see edited question: your plot also leads to the same issue) – sweetmusicality Sep 07 '17 at 18:32

Creating a reactive rectangular plot

2 Answers2