Vectors
Vectors
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Create a vector
In the chunk below, create a vector that contains the integers from one to ten. Use the c() function.
c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10):
If your vector contains a sequence of contiguous integers, you can create it with the : shortcut. Run 1:10 in the chunk below. What do you get? What do you suppose 1:20 would return?
1:10
1:20[]
You can extract any element of a vector by placing a pair of brackets behind the vector. Inside the brackets place the number of the element that you’d like to extract. For example, vec[3] would return the third element of the vector named vec.
Use the chunk below to extract the fourth element of vec.
vec <- c(1, 2, 4, 8, 16)
vec[4]More []
You can also use [] to extract multiple elements of a vector. Place the vector c(1,2,5) between the brackets below. What does R return?
vec <- c(1, 2, 4, 8, 16)
vec[c(1,2,5)]Names
If the elements of your vector have names, you can extract them by name. To do so place a name or vector of names in the brackets behind a vector. Surround each name with quotation marks, e.g. vec2[c("alpha", "beta")].
Extract the element named gamma from the vector below.
vec2 <- c(alpha = 1, beta = 2, gamma = 3)
vec2["gamma"]Vectorised operations
Predict what the code below will return. Then look at the result.
Good job! Like many R functions, R’s math operators are vectorized: they’re designed to work with vectors by repeating the operation for each pair of elements.
Vector recycling
Predict what the code below will return. Then look at the result.
Good job! Whenever you try to work with vectors of varying lengths (recall that 1 is a vector of length one), R will repeat the shorter vector as needed to compute the result.