| Attempts | Score |
|---|---|
| 1/3 | 10/10 |
What is produced at the end of this snippet of R code?
set.seed(1)
rpois(5, 2)
A vector with the numbers 1, 1, 2, 4, 1
Because the 'set.seed()' function is used, 'rpois()' will always output the same vector in this code.
> set.seed(1)
> rpois(5, 2)
[1] 1 1 2 4 1
What R function can be used to generate standard Normal random variables?
rnorm
Functions beginning with the 'r' prefix are used to simulate random variates.
Standard probability distributions in R have a set of four functions that can be used to simulate variates, evaluate the density, evaluate the cumulative density, and evaluate the quantile function.
When simulating data, why is using the set.seed() function important?
It ensures that the sequence of random numbers starts in a specific place and is therefore reproducible.
Which function can be used to evaluate the inverse cumulative distribution function for the Poisson distribution?
qpois
Probability distribution functions beginning with the 'q' prefix are used to evaluate the quantile function.
What does the following code do?
set.seed(10)
x <- rbinom(10, 10, 0.5)
e <- rnorm(10, 0, 20)
y <- 0.5 + 2 * x + e
Generate data from a Normal linear model
What R function can be used to generate Binomial random variables?
rbinom
What aspect of the R runtime does the profiler keep track of when an R expression is evaluated?
the function call stack
Consider the following R code
library(datasets)
Rprof()
fit <- lm(y ~ x1 + x2)
Rprof(NULL)
(Assume that y, x1, and x2 are present in the workspace.) Without running the code, what percentage of the run time is spent in the 'lm' function, based on the 'by.total' method of normalization shown in 'summaryRprof()'?
100%
When using 'by.total' normalization, the top-level function (in this case, `lm()') always takes 100% of the time.
When using 'system.time()', what is the user time?
It is the time spent by the CPU evaluating an expression
If a computer has more than one available processor and R is able to take advantage of that, then which of the following is true when using 'system.time()'?
elapsed time may be smaller than user time