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I am trying to make a plot in R that has a portion of the plot grey to emphasize this area. Unlike other examples, I don't want to color an area under a plot, but instead color an area on a plot starting at one area and going to the end of the graph. When I try to use rect() or polygon() it obscures the plots I want to emphasize.
For example:
x_mean <- c(1, 2, 3, 4)
y_mean <- c(1, 1, 1, 1)
y_max <- c(4, 4, 4, 4)
y_min <- c(-4, -4, -4, -4)
x_shade <- c(2, 3, 4)
y_max_shade <- c(4, 4, 4)
y_min_shade <- c(-4, -4, -4)
plot(x=rep(x_mean, 3), y=c(y_mean, y_max, y_min), bty='n', type="n" )
arrows(x0=x_mean, y0=y_min, x1=x_mean, y1=y_max, length=0)
points( x=x_mean, y=y_mean, pch=16)
This will plot 4 lines on the graph. How do I draw a grey box in the background from the 2nd line to the end of the plot?
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The polygon function can be used to shade the area under the density curve. You just need to pass the density object to it and specify a color.
Method 1: Shade a graph using polygon function : In this method, we are calling the polygon function with its argument col passed with the name or the hex code of the color needed to be shaded in the given graph.
Change R base plot point shapes To change the color and the size of points, use the following arguments: col : color (hexadecimal color code or color name). For example, col = "blue" or col = "#4F6228" .
The easiest-to-find method for shading under a normal density is to use the polygon() command. That link is to the first hit on Google for “Shading Under a Normal Curve in R.” It works (like a charm), but it is not the most intuitive way to let users produce plots of normal densities.
Just so that you're left with more than just a comment, here's a possible solution:
plot(x=rep(x_mean, 3), y=c(y_mean, y_max, y_min), bty='n', type="n" )
rect(2,-4,4,4,col = rgb(0.5,0.5,0.5,1/4))
arrows(x0=x_mean, y0=y_min, x1=x_mean, y1=y_max, length=0)
points( x=x_mean, y=y_mean, pch=16)
Note that I also demonstrated how to use alpha blending in the color specification (using rgb). This can also be useful for this sort of thing. Try moving the rect line to the end, and notice that the results still look ok, because the fill color is partially transparent.
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