Question

I have a data frame in R, and I’d like to add dummy variables in order to plot different items different colors.

My data frame, df <-, is something like this:

UID CategoryA  count
  1       AAA      2
  2       AAA      2
  3       BBB      1
  4       CCC      1
  5       DDD      1

I have another list, special <- c("AAA", "DDD")

I’d like to end up with df something like:

UID CategoryA  count dummy
  1       AAA      2     1
  2       AAA      2     1
  3       BBB      1     0
  4       CCC      1     0
  5       DDD      1     1 

So that dummy = 1, wherever CategoryA == special

I tried searching for this, but I suspect it requires %in% which is hard to google for.

I may be doing this for misguided reasons, so maybe you can help me short-circuit the problem—my objective in creating this dummy variable is to create a bar graph that’s sort of a sideways histogram listing all the categories by count. I want this variable to provide a group in order to color the ones where dummy==1 red and the ones where dummy==0 green. I’ll be using ggplot2.

Answer 1

Ugh, just after posting, I figured this out from someone answering an earlier question of mine…

df$dummy <- ifelse(df$categoryA %in% special,1,0)

For completeness, I also had to add this to my ggplot code…

scale_fill_manual(values=c("#00FFAA","#FF0000"), 
                       name="Legend",
                       breaks=c("TRUE", "FALSE"),
                       labels=c("Dummy", "No Dummy")) +