Programming Example

Vector selection by name

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💻 Practical Program

📘 Step by Step Learning

Another way to tackle the previous exercise is by using the names of the vector elements (Monday, Tuesday, ...) instead of their numeric positions. For example,

poker_vector["Monday"]

will select the first element of poker_vector since "Monday" is the name of that first element.

Just like you did in the previous exercise with numerics, you can also use the element names to select multiple elements, for example:

poker_vector[c("Monday","Tuesday")]

Instruction

Select the first three elements in poker_vector by using their names: "Monday", "Tuesday" and "Wednesday". Assign the result of the selection to poker_start.
Calculate the average of the values in poker_start with the mean() function. Simply print out the result so you can inspect it.

Program Code

# Poker and roulette winnings from Monday to Friday:
poker_vector <- c(140, -50, 20, -120, 240)
roulette_vector <- c(-24, -50, 100, -350, 10)
days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")
names(poker_vector) <- days_vector
names(roulette_vector) <- days_vector

# Select poker results for Monday, Tuesday and Wednesday
poker_start <- poker_vector[c("Monday","Tuesday", "Wednesday")]

# Calculate the average of the elements in poker_start
mean(poker_start)

Output

> # Poker and roulette winnings from Monday to Friday:
> poker_vector <- c(140, -50, 20, -120, 240)
> roulette_vector <- c(-24, -50, 100, -350, 10)
> days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")
> names(poker_vector) <- days_vector
> names(roulette_vector) <- days_vector
> 
> # Select poker results for Monday, Tuesday and Wednesday
> poker_start <- poker_vector[c("Monday","Tuesday", "Wednesday")]
> 
> # Calculate the average of the elements in poker_start
> mean(poker_start)
[1] 36.66667

Explanation

# Select poker results for Monday, Tuesday and Wednesday
poker_start <- poker_vector[c("Monday","Tuesday", "Wednesday")]

# Calculate the average of the elements in poker_start
mean(poker_start)

How to learn from this program

First read the algorithm, then study the program code line by line. After that, compare the code with the output and finally go through the explanation. This approach helps learners understand both the logic and the implementation properly.

Practice suggestion

After understanding this example, try to rewrite the same program without looking at the code. Then change some values or logic and run it again. This helps improve confidence and keeps learners engaged on the page for longer.