R as a calculator

Arithmetic operators

# Addition
2 + 2
# Subtraction
5.432 - 34234
# Multiplication
33 * 42
# Division
3 / 42
# Power
2^2
# Combine operations
((2 + 2) * 5)^2

Basic R Syntax

Whitespace does not matter

# this
head(airquality)

# is the same as this
head(
  airquality
)

Comments vs. Code

Everything that follows a # is a comment

# Look at the first rows of the built-in airquality dataset
head(airquality)

# How many rows and columns does it have?
nrow(airquality)
ncol(airquality)

• Only code is executed, comments are ignored by R
• Notes that make code more readable or add information

Variables

Store values under meaningful names to reuse them

# Create a variable
value1 <- 5
value2 <- 10
value1 + value2
#> [1] 15

Value1
#> Error:
#> ! object 'Value1' not found

Data types

The most basic data types in R:

num_vector <- c(1, 2, 3)
lgl_vector <- c(TRUE, TRUE, FALSE)
chr_vector <- c("These are", "just", "some strings")

Working with vectors

# 10 biggest cities in Europe
cities <- c("Istanbul", "Moscow", "London", "Saint Petersburg", "Berlin",
            "Madrid", "Kyiv", "Rome", "Bucharest", "Paris")

population <- c(15.1e6, 12.5e6, 9e6, 5.4e6, 3.8e6,
                3.2e6, 3e6, 2.8e6, 2.2e6, 2.1e6)

area_km2 <- c(2576, 2561, 1572, 1439, 891,
              604, 839, 1285, 228, 105)

Vector arithmetic

Arithmetic operations work element by element:

# Population density (people per km²)
population / area_km2
#>  [1]  5861.801  4880.906  5725.191  3752.606  4264.871  5298.013  3575.685
#>  [8]  2178.988  9649.123 20000.000

# Population in millions
population / 1e6
#>  [1] 15.1 12.5  9.0  5.4  3.8  3.2  3.0  2.8  2.2  2.1

Indexing vectors

Use square brackets [] to access specific elements from a vector.

cities[3]
#> [1] "London"

# Multiple elements
cities[c(1, 3, 5)]
#> [1] "Istanbul" "London"   "Berlin"

# Multiple elements (consecutive)
cities[1:3] # same as cities[c(1, 2, 3)]
#> [1] "Istanbul" "Moscow"   "London"

Functions

Functions make multiple operations available under one command.

function_name(input1, input2, ...)

The mean function

mean(c(1, 5, 6))
#> [1] 4

# Input and output can also be variables
values <- c(1, 5, 6)
result <- mean(values)
result
#> [1] 4

Missing values

NA represents a missing value in R.

values <- c(1, 5, 6, NA)
mean(values)
#> [1] NA

The function help

Access the help file of each function with ?functionName

?mean

mean(values, na.rm = TRUE)
#> [1] 4

Summary

• Variables store values: radius <- 5
• Data types: numeric, logical, character
• Vectors: collection of values of the same type, created with c()
• Indexing:
  • Single element: v[3]
  • Multiple elements: v[1:4], v[c(1, 5)]
• Functions: function_name(input1, input2, ...)
• NA are missing value → use na.rm = TRUE in functions like mean()
• Function help: ?function_name