5-7

Question 1

function to find out where NAs are located in data.

Answer 1

is.na()

Question 2

Which numbers R is representing for True and False?

Answer 2

R represents TRUE as the number 1 and FALSE as the number 0

Question 3

How to find out how many na in dataset?

What kind of answer does the function yields

Answer 3

sum(is.na(…))

True/False

Question 4

What do NA and NaN stand for?

Answer 4

not available and not a number

Question 5

Get the first 10 elements of a vector called x

Answer 5

x[1:10]

Question 6

Which sign gives us the negation of a logical expression

Answer 6

!

Question 7

if we want to create a vector called y that contains all of the non-NA| values from x(the dataset)

Answer 7

y

Question 8

y is a vector. What does y > 0 yields

Answer 8

a vector of logical values the same length as y, with TRUEs corresponding to values of y that are greater than zero and FALSEs corresponding to values of y that are less than or equal to zero.

Question 9

What do […] do

Answer 9

you want to select some particular elements (i.e. a ‘subset’) from a vector by placing an ‘index vector’ in square brackets

Question 10

subset the 3rd, 5th, and 7th elements of x

Answer 10

x[c(3,5,7)]

Question 11

if we’re interested in all elements of x EXCEPT the 2nd and 10th?

Answer 11

x[c(-2, -10)] or better: x[-c(2, 10)]

Question 12

main difference between matrices and dataframes?

Answer 12

matrices can only contain a single class of data, while data frames can consist of many different classes of data

Question 13

Can you create a sequence without c()?

Answer 13

you don’t need the c() function when using :

Question 14

Find out length of a vector

Answer 14

length() function

Question 15

What does dim() function do? Give an example for every use.

Answer 15

dim() function allows you to get OR set the dim attribute for an R object.

Question 16

row or column first in general?

Answer 16

row

Question 17

You want to create a matrix, but don´t know how. What to do?

Answer 17

?matrix

Question 18

You want to bind a character vector with names to a matrix with data

Answer 18

data.frame(patients, my_matrix). If you use cbind() you get a matrix with all being character vectors, because matrices can only take one type of data.

Question 19

you have a character string with column names, cnames, and a dataframe, my_data. You want to get the column names above the data frame. What to do?

Answer 19

colnames(my_data)