Conditional Merge in R Data Frame using a String as a search

I am prepping a database for plotting in ggplot where I will plot a large geom_point() plot. I would like one set of point to stand out and was thinking of making a dummy column so that I could use that column as a color variable as in:

p <- ggplot(data, aes(x-x,y-y,color=color)
colors=c("yes"="orange2", "no"="grey")
scale_color_manual(values=colors)
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to make the dummy column I wanted to do as follows:

df$color <- "no"

to set the default color, and then use a grep substitute to make a highlight color.

df$color[grep("string", df$V1, ignore.case=T),] < "yes"

where V1 is a column that contains the string I would like to substitute. Although I would love some suggestions on how to get the substitution I would also be interested in learning about a more direct coloring method that would involve highlighting data of a particular value.

thanks

Here is one way to do it using grepl. I am using the mtcars data set for illustrative purposes. Say you want Merc to stand out. You can call

ggplot(mtcars, aes(mpg, hp)) +
  geom_point(aes(colour = grepl('Merc', rownames(mtcars)))) +
  scale_colour_manual("Merc", values = c('black', 'red'))