Programming/R
R is a language used for statistics.
Comments
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Variables
Variables R are loosely typed in R. That means that the type (bool, int, string, etc) is implicitly declared by the value provided.
Variable Definition
a_bool <- TRUE b_bool <- FALSE my_var_1 <- "This is " my_var_2 <- "a string."
Variable Usage
# We can print our variables by retyping the variable name with no further syntax. a_bool b_bool my_var_1 my_var_2
Variable Types
Variable types in R are called the following:
- Booleans are called
Logicals. - Text is called
characters. - Numbers are called
numerics.
If ever unsure you can check the typing of a variable with class() . For example:
# This will print out the typing for "my_variable". class(my_variable)
Basic Data Structures
Vectors
In R, "Vectors" are what most other languages call "Arrays".
Arrays (vectors) in R are similar to Arrays (lists) in Python. That is, the size and semantics of the array are taken care of for you, and all you need to worry about are the values you place into it.
For the rest of this section, R arrays will be referred to by the proper name, aka Vectors.
Declaring Vectors
# Vectors in R can have mixed value types.
character_vector <- c("This", "is", "a", "character", "vector")
numeric_vector <- c(1, 2, 15, 6)
logical_vector <- c(TRUE, FALSE, FALSE)
mixed_vector <- c(TRUE, 1, "test")
Accessing Vector Values
Unlike most other programming languages, indexes in R start at 1.
my_vector <- c(5, 7, 2) # Print first index. my_vector[1] # Print last index. my_vector[3]
Furthermore, unlike most languages, you can select multiple values at once by using a nested Vector syntax:
my_vector <- c(5, 7, 2) # Print out first and last index at the same time. my_vector[c(1, 3)] # Alternatively, to select a range of values, we can use this syntax. # In this case, we print out the first two indexes. my_vector[1:2]
Manipulating Vectors
Mathematical functions on Vectors handle very similarly to how you would expect real Mathematical Vectors to handle. Template:ToDo
For example, adding two vectors will combine the corresponding index values.
my_vector <- c(1, 2, 3) ones_vector <- c(1, 1, 1) # This should create a new vector of (2, 3, 4). new_vector <- my_vector + ones_vector
Alternatively, if you want to combine all values in a vector, use the sum() function.
my_vector <- c(1, 2, 3) # This will output "6". sum(my_vector)
To get an average of array values, we can use the mean() function.
my_vector <- c(1, 2, 3) # This will output "2". mean(my_vector)
We can also test equality on every value within a Vector.
my_vector <- c(1, 2, 3) # Check which values are greater than 1. my_vector > 1
We can take equality testing a bit further, to only print the values that met our criteria.
my_vector <- c(9, 10, 7, 11, 5, 12) # Save which values are greater than 10. selection_vector <- my_vector > 10 # Print out only values greater than 10. This should print out (11, 12). my_vector[selection_vector]
Dictionaries
Dictionaries in R appear to actually be modified vectors. Basically, first create your desired vector (to hold the "values"), then use the names function on it to declare keys.
Here's an example for a hypothetical business trying to track count of items sold.
product_sold <- c(50, 56, 102)
names(product_sold) <- c("Ice Cream", "Burgers", "Pizza")
Alternatively, you can create two arrays and combine them.
product_sold <- c(50, 56, 102)
product_names <- c("Ice Cream", "Burgers", "Pizza")
names(product_sold) <- product_names
The two above code snippets should be equivalent.
Once we have names (aka keys) associated with our values, we can use those to get specific indexes.
# Print out the count of pizza sold. product_sold["Pizza"]