Assignment and Recycling Rule in R Programming

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Questions and Answers

What happens when a logical vector of indices is used to subset a vector and the lengths do not match?

The logical vector is recycled. (correct)
An error is returned.
Only the first element is subsetted.
The subset is empty.

What does the output 'integer(0)' mean in the context of subsetting?

The subset contains only NA values.
An error occurred.
The subset contains all elements.
The subset is empty. (correct)

What is the purpose of the 'is.na' function?

To convert a vector to a different type.
To detect non-missing values.
To replace missing values with a default value.
To detect missing values. (correct)

How can we use the 'is.na' function to subset the non-missing values of a vector?

By using the 'is.na' function to create a logical vector and then subsetting. (D) Signup and view all the answers

What is the result of the expression 'x[(x > 4) & (x < 2)]'?

An empty subset. (B) Signup and view all the answers

What is the correct way to detect missing values in a vector?

Using the 'is.na' function. (D) Signup and view all the answers

What is the result of the expression 'z[z^2 > 8]'?

A subset of z containing elements whose square is greater than 8. (B) Signup and view all the answers

What is the purpose of recycling a logical vector of indices when subsetting a vector?

To repeat the logical vector until it matches the length of the vector being subsetted. (B) Signup and view all the answers

What happens to the values in the vector `counts` when `counts[c(1:3, 7:9)] = NA` is executed?

The values in the indices <code>c(1:3, 7:9)</code> are replaced with <code>NA</code>. (A) Signup and view all the answers

What is the length of the vector `counts[c(1:3, 7:9)]` after executing `counts[c(1:3, 7:9)] = NA`?

6 (D) Signup and view all the answers

What is the result of `c(NA, 99)` when applied to the subset `counts[c(1:3, 7:9)]` using the assignment operator?

The values in <code>counts[c(1:3, 7:9)]</code> are replaced with <code>NA</code> and <code>99</code> in a repeating pattern. (D) Signup and view all the answers

What is the difference between a numeric vector and a logical vector?

A numeric vector contains numbers, while a logical vector contains either <code>TRUE</code> or <code>FALSE</code>. (B) Signup and view all the answers

How can you create a logical vector of length 7 containing only `TRUE` values?

<code>rep(TRUE, 7)</code> (A) Signup and view all the answers

What is the result of the expression `x >= 7` applied to the numeric vector `x = 1:10`?

A logical vector of length 10 with <code>TRUE</code> for values greater than or equal to 7, and <code>FALSE</code> for others. (A) Signup and view all the answers

In the example `sum(x >= 7)`, what does the value 4 represent?

The number of elements in the vector <code>x</code> that are greater than or equal to 7. (C) Signup and view all the answers

In the example `mean(x >= 7)`, what does the value 0.4 represent?

The proportion of elements in the vector <code>x</code> that are greater than or equal to 7. (D) Signup and view all the answers

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Study Notes

The Recycling Rule

The recycling rule applies to assignment, in addition to arithmetic and conditional operators
When assigning a vector to a subset, the vector is replicated to match the subset length if necessary
Example: counts[c(1:3, 7:9)] = NA replicates NA six times to match the subset length
Example: counts[c(1:3, 7:9)] = c(NA, 99) replicates c(NA, 99) three times to match the subset length

Logical Vectors

Logical vectors are composed of logical values (TRUE, FALSE, or NA)
Example: c(TRUE, FALSE, FALSE) creates a logical vector
Replication: rep(TRUE, 7) creates a logical vector with seven TRUE values
Conditional operators can be applied to numeric or character vectors to create logical vectors
Example: x >= 7 creates a logical vector from a numeric vector x
Important property: logical vectors are automatically converted to numeric vectors when arithmetic operations are applied, where TRUE becomes 1 and FALSE becomes 0
Examples: TRUE + FALSE equals 1, sum(x >= 7) equals 4, and mean(x >= 7) equals 0.4

Subsetting with Logical Vectors

Logical vectors can be used as indices for subsetting
When using a logical vector as an index, the subset contains elements in the same positions as the TRUE elements in the index
Example: counts[c(TRUE, FALSE, TRUE, FALSE, FALSE)] subsets counts using a logical vector of indices
Example: counts[counts < 3] subsets counts using a logical vector of indices created from the same vector

Subsetting with Logical Expressions

Logical expressions can be used to subset vectors
Example: x[(x > 4) | (x < 2)] subsets x using a logical expression
Example: x[(x > 4) & (x < 2)] subsets x using a logical expression
Output integer(0) means no elements satisfy the condition
Example: z[z^2 > 8] subsets z using a logical expression involving a conditional operator and arithmetic operation

Missing Values

The is.na function detects missing (NA) values in a vector
The function returns a logical vector with TRUE in place of NA values and FALSE in place of non-NA values
Example: is.na(x) detects missing values in vector x
is.na can be used to subset non-missing values of a vector

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