How to color points in a different color if a data attribute is not null

问题

I have a scatter plot in R (with ggplot2). The data has a numeric column (let's call it bin) which can contain various integer values or null.

I would like to colour the points with non-null bin values differently from the others. I do not want to one colour per value of bin, that would be too noisy. Just simply, say, red for those with a non-null bin and black for the others.

qplot has a colour attribute, but I don't know how to express a condition like colour = bin != null ? "red" : "black"

回答1:

You could define the color first:

color <- rep("black", length(bin))
color[is.null(color)] <- "red"

Otherwise you can use an ifelse statement:

colour=ifelse(is.null(bin), "red", "black")

来源：https://stackoverflow.com/questions/2376034/how-to-color-points-in-a-different-color-if-a-data-attribute-is-not-null