R Programming Questions and Answers – Subsetting – 2

This set of R Programming Questions and Answers for experienced focuses on “Subsetting – 2”.

1. Which of the following extracts first element from the following R list?

 > x <- list(foo = 1:4, bar = 0.6)

a) x[[1]]
b) x[1]
c) x[[0]]
d) x[0]
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2. Point out the correct statement?
a) You can also use the $ operator to extract elements by name
b) $ operator can be used with computed indices
c) The [[ operator can only be used with literal names
d) $ operator semantics are similar to that of [[
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3. What will be the output of the following R code?

> x <- list(foo = 1:4, bar = 0.6, baz = "hello")
> name <- "foo"
> x$name

a) 1
b) 2
c) 3
d) NULL
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4. What will be the output of the following R code?

> x <- list(foo = 1:4, bar = 0.6, baz = "hello")
> name <- "foo"
> x[[name]]

a) 1 2 3 4
b) 0 1 2 3
c) 1 2 3 4 5
d) All of the mentioned
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5. What will be the output of the following R code?

> x <- list(a = list(10, 12, 14), b = c(3.14, 2.81))
> x[[c(1, 3)]]

a) 13
b) 14
c) 15
d) 18
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6. What will be the output of the following R code?

> x <- list(aardvark = 1:5)
> x$a

a) 1 2 3 4 5
b) 2 3 5
c) 1 3 3 5
d) 1 2 3
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7. Which of the following code extracts 1st element of the 2nd element?

 > x <- list(a = list(10, 12, 14), b = c(3.14, 2.81))

a) x[[c(2, 1)]]
b) x[[c(1, 2)]]
c) x[[c(2, 1,1)]]
d) x[[(2, 2,1)]]
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8. What will be the output of the following R code?

> x <- list(aardvark = 1:5)
> x[["a", exact = FALSE]]

a) 1 2 3 4 5
b) 2 3 5
c) 1 3 3 5
d) 1 2 3
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9. What will be the output of the following R code?

> x <- c(1, 2, NA, 4, NA, 5)
> bad <- is.na(x)
> print(bad)

a) FALSE FALSE FALSE FALSE TRUE FALSE
b) FALSE TRUE TRUE FALSE TRUE FALSE
c) FALSE FALSE TRUE FALSE TRUE FALSE
d) FALSE TRUE TRUE TRUE TRUE FALSE
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