Analyzing large data sets with the R package
Objective: to acquire skills in statistical data processing and graphics using the R programming language.
Objectives: to get acquainted with the interface and functionality of R, to learn how to process, analyze, and visualize various types of data using the R package.
Methodological recommendations
1. Familiarize yourself with the R program andRStudio.
R is a programming language for statistical processing, data analysis, and graphics, as well as a free and open-source computing environment as part of the GNU project. R supports a wide range of statistical and numerical methods and powerful additional functional and analytical capabilities (built-in package library). Packages are libraries for specific functions or special applications. R comes with a basic set of packages. As of 2019, there are more than 12,000 packages available.
R is widely used in the social sciences, statistics, economics, insurance, sociology, finance, physics, etc.
R is available for all operating systems, including Linux, Mac OS, and Windows.
R is a matrix, object-oriented programming language. This means that, in theory, anything can be saved as an R object. Each object has its own class that describes what this object contains and what each function can do with this data. For example, plot(x) produces one result if x is a regression and another if it is a vector.
The R package can be downloaded and installed absolutely free of charge. To do this, visit the CRAN website (https://cran.r-project.org) and download the installation package. After running it, you need to select the appropriate installation parameters (language, package components, and other
settings). After the program starts, a dialog box opens - the console window, where all commands and the results of their execution are displayed (Fig. 165).
Figure 165. The dialog box (console) for starting the R package
To make it easier for the user to work with the R package, an interface program called RStudio was created. Note that working with R and RStudio is almost identical. For example, RStudio provides many convenient tools, and it has a pleasant and more understandable interface. To download it, you must first install the R package and then download the corresponding file:
https://www.rstudio.com/products /rstudio/download /#download.
After launching the program, a window consisting of 4 blocks will open (Fig. 166). The RStudio environment consists of windows:
1) script (for writing code and preparing it for launch);
2) console (displays all commands and the results of their execution);
3) Workspace (Environment) - to display all objects and their descriptions. The History tab shows the history of commands entered by the user;
4) Files (displays the working directory - folder), Plots (for visualizing all charts), Packages (shows all installed library packages), Help (for reference information).
Figure 166. The RStudio startup dialog box
For example, using the R package as a regular calculator, we can write certain mathematical actions in the script window and press the Run button or use the Cntr + Enter button combination (Figure 167).
Figure 167. Performing simple calculations in RStudio
After executing the code, the calculation result appeared in the console window, and the History tab simultaneously displayed all the commands that the user entered.
All functions are entered accordingly.
If you don't know what kind of function you are working with, you should call up the help. To do this, in the script. window, enter a question mark before the function name and click the Run button. All the necessary reference information will be displayed in the Help window (tab) (Figure 168).
Figure 168. Launching help in RStudio
The user can create variables. To do this, enter the variable designation in the console window, then the assignment sign (<-) and the value to which it corresponds. For example, y = 100 (Fig. 169).
Figure 169. Creating a variable in RStudio
The Environment window displays the result of creating the variable. You can also perform. calculations (y*2) and create expressions (x = y^2) (Figure 170).
Figure 170. Simple calculations in RStudio
In R, any command is a function that can be passed as an argument. Functions can be easily combined.
The assignment symbol is "<-". You can also use the wildcard "=". That is, the following two expressions are equivalent:
> а <- 2; > а = 2.
Arguments are given in parentheses.
Usually, it is better to use quotation marks for names, but it is not always necessary.
"#" is used for comments.
Commands are separated by a semicolon ";" or a carriage return character. If you want to place more than one expression on one line, you must use the ";" separator.
R is case sensitive: "a" and "A" are two different objects, so all functions and arguments must be entered in lowercase.
Traditionally, the underscore character "_" is not used in names. In most cases, it is better to use the dot character ".". Avoid using the underscore character as the first character in an object name.
There are special characters in R: NA: Not Available;
NaN: Not a Number, for example, uncertainty 0/0; Inf: Infinity; -Inf: (Minus infinity).
You can exit R using q (). The no argument means that the session is not to be saved.
The R package works with the following data types: logical, integer, real, complex, character, and list.
The analytical capabilities of the R package are due to the ability to work with various objects, in particular:
1. Vectors are the most basic of R objects, and can contain only one type of data. You can create a vector by using the c () function, which combines several elements of the same type. You can also create a sequence using the: symbol or the seq () function. For example, 1:5 creates a vector sequence of numbers from 1 to 5. The seq () function allows you to specify the interval between numbers. You can repeat the pattern using the rep () function. You can also create a numeric vector with missing values by using the numeric () function, or a character vector with character () or a logical vector with logical ().
2. Factors are similar to vectors, but with a defined set of levels. Factor represents a nominal or rank scale. It is used to represent Y in classification models, and the factor () function transforms a vector into a factor. Also, factor can be sorted using the option ordered = T or the function ordered ().
3. Matrices are similar to vectors, but with specific instructions for output. A matrix is a two- dimensional set of elements of the same type (table). If you want to create a matrix, one way is to use the matrix () function. You enter a vector, a set ofrows or columns, and you can tell R how to interpret the data (by default, as columns).
The cbind () and rbind () functions combine vectors in a matrix by column or by row. The dimension of the matrix can be obtained using the dim () function. Otherwise, the nrow () and ncol () functions return the number of rows and columns, respectively.
4. Arrays are similar to matrices, but can have more than two dimensions. An array is a multidimensional set of elements of the same type. Array.
must be symmetrical in all dimensions. The vector objects that make up t h e array must be of the same type, but not necessarily of numeric type.
5. A list is a vector for R objects. Lists area collection of R objects. The list () function creates a list; unlist () transforms a list into a vector. Mostly, it is convenient to store in the form of lists either some data of the same type that corresponds to different iterations, for example, many models, or to store heterogeneous data that have a semantic connection, for example, different statistical characteristics of a single model.
6. A dataframe is similar to a matrix, but does not require all columns to be identical in type. The structure is a list of variables/vectors of the same length. Data.frame - a two-dimensional data set (table). Unlike matrices, columns in a data.frame can contain data of different types. However, there can be only one data type within each column. This is because a data.frame is a list of vectors (columns). Therefore, different functions can be applied to thedata.frame.
7. Formulas area special form. of expressing relationships between variables in an equation. Formulas are used when building models to determine the functional relationship between parameters. The dot symbol "(.)" replaces all available variables.
8. Classes is a data type for a variable, and a variable of this type is an object - an instance of the class). Classes are attached to objects as attributes. All objects in R have their own class, type, and dimension.
All objects support naming the elements they contain. To do this, use the character " or ''. Similarly to vectors, matrices and data.frames have such properties as rownames and colnames, which allow you to change the names of columns and rows.
To delete names, you can assign a special type NULL.
Converting data types is done through a group of functions that are based on as.
Indexing in R is an effective and powerful tool for working with data. Indexes can be numeric, boolean, and textual.
Three types of expressions are used for indexing: [ - selects elements of a vector/list/array, etc;
$ - selects one element from the data.frame/list by its name;
[[- selects elements from a vector/list/array, etc. but discards names if they exist.
The indexing features allow you to change the position of items and duplicate them. To delete elements by index value, a minus sign is added before them. To add a new element (column/row in the data.frame) to the list, anew name or numeric index is used.
If an index is accessed that does not exist, the special value NA is returned.
2. Working in RStudio: graphical features.
Before you start working in RStudio, you need to import data. To enter data, in addition to the manual mode, you can use the Environment window, the Inport Dataset button, and specify what type of file to import and where from. Weremind you that the filename must be in English and consist of one word (Fig. 171).
Figure 171. Importing data into RStudio
The result is a data table containing information about the age and salary of the bank's customers (Figure 172).
Figure 172. Input data for analysis in RStudio
If you want to name the columns or change them, goto the Untitled*1 script window and run the command:
colnames(Salary)<-c('Age_years','Wage_th_UAH').
As a result, we get new names for the table columns (Figure 173).
Figure 173. Changing the names of table columns in RStudio
The R package (RStudio) has a powerful visualization unit. To work with graphics in R, you need to install the appropriate package - ggplot2, that is, run the install.packages ("ggplot2") command or select the Graphics package in the library and click the Install button.
In ggplot2, any type of infographic is the result of the interaction of a number of elements:
1) of the data array;
2) schemes of correspondence of variables to the array of visual means (aesthetic);
3) geometric object (geom);
4) statistical transformation (stat);
5) coordinate system (coord);
6) guide;
7) panels (facet);
8) artistic design (theme).
Visualize the original information space. To do this, use the command: plot(Salary$Age_years,Salary$Wage_th_UAH) (Fig. 174).
Figure 174. Building a chart in RStudio
The user can also change the parameters of the dot diagram: select the type, color, and thickness. To do this, run the command: plot(Salary$Age_years,Salary$Wage_th_UAH,col='red',lwd=2) (Fig. 175).
Figure 175. Editing a graph in RStudio
To change the axis labels and name the dot plot, run the following command: plot(Salary$Age_years,Salary$Wage_th_UAH,col='red',lwd
=2,xlab = 'Age_of_Bank_Customers',ylab = 'Salary_thousand_hryvnias',main = 'Dependence_of_income_on_age') (Fig. 176).
Figure 176. Finished visualization in RStudio
The user can also change the type of chart. For example, let's turn a dot chart into a bar chart. To do this, you need to change the geometric object to aes(xlab = 'Age of bank customers'
= cyl)) + geom_bar()+ coord_polar().
So, the source data has been downloaded and visualized.