Visualizing Patterns over Time - Data Points: Visualization That Means Something - page 100

To do this, you need to build a list, or vector in R, of colors. Visit each year
and decide what color to make the corresponding bar. If it's a win for the
United States, specify red. Otherwise, specify gray. Here's the code to
do that:

fill_colors <- c()
for ( i in 1:length(hotdogs$Country) ) {
if (hotdogs$Country[i] == “United States”) {
fill_colors <- c(fill_colors, “#821122”)
} else {
fill_colors <- c(fill_colors, “#cccccc”)
}
}

The first line starts an empty vector named fill_colors . You use c() to cre-
ate vectors in R.

The next line starts a for loop. You can tell R to loop through an index
named i from 1 to the number of rows in your hotdogs data frame. More
specifically, you can take a single column, Country , from the hotdogs data
frame, and find the length. If you were to use length() with just hotdogs,
you would get the number of columns, which is 5 in this case, but you want
the number of rows, which is 31 . There is one row for each year from 1980
to 2010, so the loop will execute the code inside the brackets 31 times, and
for each loop, the i index will go up one.

Most languages use
0-based arrays or
vectors where
the first item is
referenced with
a 0-index. R,
however, uses
1-based vectors.

So in the first iteration, where i equals 1, check if the country in the first
row (that is, winner for 1980) is the United States. If it is, append the color
#821122 , which is a reddish color in hexadecimal form, to fill_colors .
Otherwise, append # cccccc , which is a light gray.

In 1980, the winners were from the United States, so do the former. The
loop checks 30 more times for the rest of the years. enter fill_colors in
the R console to see what you end up with. It's a vector of colors just like
you want.

Pass the fill_colors vector in the col argument for barplot() like so.
barplot(hotdogs$Dogs.eaten, names.arg=hotdogs$Year, col=fill_colors,
border=NA, xlab=”Year”, ylab=”Hot dogs and buns (HDB) eaten”)

The code is the same as before, except you use fill_colors instead of “red”
in the col argument.