Creating objects in R

weight_kg <- 55

When assigning a value to an object, R does not print anything. You can force R to print the value by using parentheses or by typing the object name:

weight_kg <- 55    
(weight_kg <- 55)  
## [1] 55
weight_kg          
## [1] 55

For instance, we may want to convert this weight into pounds (weight in pounds is 2.2 times the weight in kg):

We can also change an object’s value by assigning it a new one:

For example, let’s store the animal’s weight in pounds in a new object, weight_lb:

and then change weight_kg to 100.

R executes code in top-down order. So what happens on line 10 occurs before line 11. What do you think is the current content of the object weight_lb? 126.5 or 220?

write your answer here

Functions and their arguments

Let’s look into the round function.

We see that if we want a different number of digits, we can type digits = 2 or however many we want.

If you provide the arguments in the exact same order as they are defined you don’t have to name them:

And if you do name the arguments, you can switch their order:

Data Types

R objects come in different data types.

Numbers

Letters

Boolean

Data Structures

Vectors

For example we can create a vector of animal weights and assign it to a new object weight_g:

A vector can also contain characters:

You can use the function class() to see what data type a vector is.

If you combine letters and numbers, everything will be treated as characters.

Doing math on vectors

You can perform math operations on the elements of a vector such as

When adding two vectors together, the elements in the same position are added to each other. So element 1 in the vector a is added to element 1 in vector b.

More complex calculations can be performed on multiple vectors.

All these operations on vectors behave the same way when dealing with variables in a data set (data.frame).

If you want to add the values within a vector, you use functions such as sum(), max() and mean()

Subsetting vectors

If we want to extract one or several values from a vector, we must provide one or several indices in square brackets. For instance:

The number in the indices indicates which element to extract. For example we can extract the 3rd element in weight_g by typing

Conditional subsetting

Typically, these logical vectors are not typed by hand, but are the output of other functions or logical tests such as:

For instance, if you wanted to select only the values where weight in grams is above 50 we would type:

You can combine multiple tests using & (both conditions are true, AND) or | (at least one of the conditions is true, OR):

Weight is less than 30g or greater than 60g

Weight is between 60 and 80lbs

The function %in% allows you to test if any of the elements of a search vector are found:

Order matters.

When considering string or character vectors or data elements, R treats everything in alphabetical order.

Data Frames

We can load the diamonds data set into our global environment by typing

We can get an idea of the structure of the data frame including variable names and types by using the str function,

Inspecting data.frame objects

Identifying variables

Below is an example of finding the average price for all diamonds in the data set.

Here is an example of finding the average price for Good quality diamonds.