Hands-On Programming with R

Chapter 5. Modifying Values

Are you ready to play some games with your virtual deck? Not so fast! The point system in your deck of cards doesn’t align well with many card games. For example, in war and poker, aces are usually scored higher than kings. They’d have a point value of 14, not 1.

In this task, you will change the point system of your deck three times to match three different games: war, hearts, and blackjack. Each of these games will teach you something different about modifying the values inside of a data set. Start by making a copy of deck that you can manipulate. This will ensure that you always have a pristine copy of deck to fall back on (should things go awry):

deck2 <- deck

Changing Values in Place

You can use R’s notation system to modify values within an R object. First, describe the value (or values) you wish to modify. Then use the assignment operator <- to overwrite those values. R will update the selected values in the original object. Let’s put this into action with a real example:

vec <- c(0, 0, 0, 0, 0, 0)
vec
##  0 0 0 0 0 0

Here’s how you can select the first value of vec:

vec[1]
##  0

And here is how you can modify it:

vec[1] <- 1000
vec
## 1000    0    0    0    0    0

You can replace multiple values at once as long as the number of new values equals the number of selected values:

vec[c(1, 3, 5)] <- c(1, 1, 1)
vec
##  1 0 1 0 1 0

vec[4:6] <- vec[4:6] + 1
vec
## 1 0 1 1 2 1

You can also create values that do not yet exist in your object. R will expand the object to accommodate ...