Arithmetics
Addition |
+ |
Subtraction |
- |
Multiplication |
* |
Division |
/ |
Modulo |
%% |
Exponentiation |
^ |
Modulo returns the remainder of the division of the number to the left by the number on its right, for example 5 modulo 3 or 5 %% 3 is 2.
Comparison operators
Less than |
< |
More than |
> |
Less than or equal to |
<= |
Greater than or equal to |
>= |
Equal to each other |
== |
Not equal to each other |
!= |
Selecting by comparison
# Poker and roulette winnings from Monday to Friday:
poker_vector <- c(140, -50, 20, -120, 240)
roulette_vector <- c(-24, -50, 100, -350, 10)
days_vector <- c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")
names(poker_vector) <- days_vector
names(roulette_vector) <- days_vector
# Which days did you make money on roulette?
selection_vector <- roulette_vector > 0
# Select from roulette_vector these days
roulette_winning_days <- roulette_vector[selection_vector]
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Data Types
Decimal values |
4.5 |
Numerics |
Whole numbers |
4 |
Integers |
Boolean values |
TRUE / FALSE |
Logical |
Text / String |
"Text" |
Characters |
Show the data type: class(data)
Lists
Create a list |
my_list <- list(element1, element2) |
Give names to the list items |
my_list <- list(name1 = your_comp1, name2 = your_comp2) |
# Adapt list() call to give the components names
my_list <- list(vec = my_vector,
mat = my_matrix,
df = my_df)
#or if the list was alread created
names(my_list) <- c("vec", "mat", "df")
Selecting components in a list
One way to select a component is using the numbered position of that component. For example, to "grab" the first component of shining_list you type
shining_list[[1]]
A quick way to check this out is typing it in the console. Important to remember: to select elements from vectors, you use single square brackets: [ ]. Don't mix them up!
You can also refer to the names of the components, with [[ ]] or with the $ sign. Both will select the data frame representing the reviews:
shining_list[["reviews"]]
shining_list$reviews
Besides selecting components, you often need to select specific elements out of these components. For example, with shining_list[[2]][1] you select from the second component, actors (shining_list[[2]]), the first element ([1]). When you type this in the console, you will see the answer is Jack Nicholson. |
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Vector Basics
Assign value to variable |
my_var <- 4 |
Numeric vector |
numeric_vector <- c(1, 10, 49) |
Character_vector |
character_vector <- c("a", "b", "c") |
Boolean vector |
boolean_vector <- c(TRUE, FALSE, TRUE) |
Naming a vector |
names(numeric_vector) <- c("Jack", "Jill", "Johanna") |
Sum of the elements in the vector |
sum(vector_name) |
Select element 3 of the vector |
element <- vector_name[3] |
Select elements 2, 3, 4, 5 of the vector |
elements <- vector_name[3:5] |
Factors
# Animals - Turn vector character elements into nominal factors
animals_vector <- c("Elephant", "Giraffe", "Donkey", "Horse")
factor_animals_vector <- factor(animals_vector)
factor_animals_vector
# Temperature - Turn vector character elements into ordinal factors
temperature_vector <- c("High", "Low", "High","Low", "Medium")
factor_temperature_vector <- factor(temperature_vector, order = TRUE, levels = c("Low", "Medium", "High"))
factor_temperature_vector
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When factors are ordinal::
order = TRUE
To give the order of the ordinal factors:
levels = c("Low", "Medium", "High"))
Data Frames
Show the first couple of lines |
head(data_frame) |
Show the last couple of lines |
tail(data:frame) |
Summarize data frame (min, max, median, quartiles) |
summary(data_frame) |
Structure (nr. obs, var., names, data type...) |
str(data_frame) |
unlike matrixes, df can have different types of data - BUT all variables need to have the same length (unlike for lists)
Create data frame from vectors + select values
# Definition of vectors
name <- c("Mercury", "Venus", "Earth",
"Mars", "Jupiter", "Saturn",
"Uranus", "Neptune")
type <- c("Terrestrial planet",
"Terrestrial planet",
"Terrestrial planet",
"Terrestrial planet", "Gas giant",
"Gas giant", "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532,
11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03,
0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)
# Create a data frame from the vectors
planets_df <- data.frame(name, type, diameter, rotation, rings)
# Select first 5 values of diameter column
planets_df[1:5, "diameter"]
# Select the rings variable from planets_df
rings_vector <- planets_df$rings
# Select planets with diameter < 1
subset(planets_df, subset = diameter <1)
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Order the data
In data analysis you can sort your data according to a certain variable in the dataset. In R, this is done with the help of the function order().
order() is a function that gives you the ranked position of each element when it is applied on a variable, such as a vector for example:
a <- c(100, 10, 1000)
order(a)
[1] 2 1 3
10, which is the second element in a, is the smallest element, so 2 comes first in the output of order(a). 100, which is the first element in a is the second smallest element, so 1 comes second in the output of order(a).
This means we can use the output of order(a) to reshuffle a:
a[order(a)]
[1] 10 100 1000 |
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Matrices
Construct Matrix with 3 rows that contain the numbers 1 to 9 |
matrix(1:9, byrow = TRUE, nrow = 3) |
From Vector to Matrix |
Matrix_names <- matrix(vector_name, byrow = TRUE, nrow = 3) |
Totals for each row of a matrix |
rowSums(my_matrix) |
Total for each row of a matrix |
colSums() |
Adding columns |
big matrix <- cbind(vector1, matrix1) |
Adding rows |
rbind |
Select all elements of the first column |
matrix[,1] |
Select all elements of the first row |
matrix[1,] |
Select 2nd element of 3rd column |
matrix[2,3] |
Create matrix with the data on the rows 1, 2, 3 and columns 2, 3, 4. |
matrix[1:3,2:4] |
Average of the matrix elements |
mean(matrix_name) |
Summary of Matrix (and other stuff) |
summary(matrix_name) |
The argument byrow indicates that the matrix is filled by the rows. If we want the matrix to be filled by the columns, we just place byrow = FALSE
all data in a matrix should be of the same type. Otherwise, create a data frame
Naming a Matrix
# Box office Star Wars (in millions!)
new_hope <- c(460.998, 314.4)
empire_strikes <- c(290.475, 247.900)
return_jedi <- c(309.306, 165.8)
# Construct matrix
star_wars_matrix <- matrix(c(new_hope, empire_strikes, return_jedi), nrow = 3, byrow = TRUE)
# Vectors region and titles, used for naming
region <- c("US", "non-US")
titles <- c("A New Hope", "The Empire Strikes Back", "Return of the Jedi")
# Name the columns with region
colnames(star_wars_matrix) <- region
# Name the rows with titles
rownames(star_wars_matrix) <- titles
# Print out star_wars_matrix
star_wars_matrix
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