16. Functions by Chapter

Author

Affiliation

Smit, A. J.

University of the Western Cape

Published

January 1, 2021

Useful information

…incomplete…

Operators

There are several operators you can use to help build expressions as shown in Table $???$ .

Functions

Some example functions covered so far are presented in Table $???$ .

Some summary functions are presented in Table $???$ .

Reuse

CC BY-NC-SA 4.0

Citation

BibTeX citation:

@online{smit,_a._j.2021,
  author = {Smit, A. J.,},
  title = {16. {Functions} by {Chapter}},
  date = {2021-01-01},
  url = {http://tangledbank.netlify.app/BCB744/intro_r/16-functions.html},
  langid = {en}
}

For attribution, please cite this work as:

Smit, A. J. (2021) 16. Functions by Chapter. http://tangledbank.netlify.app/BCB744/intro_r/16-functions.html.

--- date: "2021-01-01" title: "16. Functions by Chapter" --- ## Useful information ...incomplete... ### Operators There are several operators you can use to help build expressions as shown in Table \ref{tab:operators}. \begin{table}[htbp] \begin{small} \begin{center} \caption{Logical operators for use in R.} \label{tab:operators} \newcolumntype{R}{>{\raggedright\arraybackslash}X}% \begin{tabularx}{\textwidth}{l X l} \toprule Operator & Meaning & Example \\ \midrule \texttt{\textless{}} & less than & \texttt{x\ \textless{}\ 3} \\ \texttt{\textgreater{}} & greater than & \texttt{x\ \textgreater{}\ 5} \\ \texttt{\textgreater{}=} & greater than or equal to & \texttt{x\ \textgreater{}=\ 24} \\ \texttt{\textless{}=} & less than or equal to & \texttt{x\ \textless{}=\ 19} \\ \texttt{==} & exactly equal to & \texttt{x\ ==\ 666} \\ \texttt{!=} & not equal to & \texttt{x\ !=\ 777} \\ \texttt{\&} & AND; returns TRUE if statements on both sides of the \texttt{\&} are TRUE & \texttt{(x\ \textgreater{}\ 3)\ \&\ (y\ !=\ 5)} \\ \texttt{\textbar{}} & OR; the pipe symbol \texttt{\textbar{}}; TRUE if a statement on either side of the \texttt{\textbar{}} is TRUE & \texttt{(x\ \textless{}\ 10)\ \textbar{}\ (x\ \textgreater{}\ 20)} \\ \bottomrule \end{tabularx} \end{center} \end{small} \end{table} \begin{mybox}{}{Question} The logical AND: If we had said \texttt{subset(dat, site == "Kommetjie" \& site == "Baboon")}, what would have happened? Why? Try it and see... \end{mybox} ### Functions Some example functions covered so far are presented in Table \ref{tab:functions}. \begin{table}[htbp] \begin{small} \begin{center} \caption{Common functions used for daily work in R.} \label{tab:functions} \newcolumntype{R}{>{\raggedright\arraybackslash}X}% \begin{tabularx}{\textwidth}{R l R R } \toprule \textbf{Type} & \textbf{Function} & \textbf{What it does} & \textbf{Syntax} \\ \midrule Checking a dataframe & \texttt{class()} & Gives the class (type of data structure) of the object & \texttt{class(dat)} \\ Numerical calculations & \texttt{mean()}, \texttt{sd()} & Calculations on a numerical R object (variables, vectors, arrays) & \texttt{mean(dat\$var)} \\ Gets working directory & \texttt{getwd()} & Gets current working directory & \texttt{getwd()} \\ Sets working directory & \texttt{setwd()} & Sets working directory to specified path & \texttt{setwd("yourpath")} \\ Getting your data into R & \texttt{read.table()} & Reads file in table format (with specified separator sep) and creates a dataframe from it & \texttt{read.table("filename.csv", header= TRUE, sep = ",")} \\ Getting .csv file into R & \texttt{read.csv()} & Reads in .csv file to a dataframe; as above, but `sep' predefined & \texttt{read.csv("filename.csv", header= TRUE)} \\ List variables & \texttt{ls()} & Lists objects in memory & \texttt{ls()} \\ Variable names in dataframe & \texttt{names()} & Gives variable names & \texttt{names(dat)} \\ Subsetting a dataframe & \texttt{subset()} & Subset a dataframe & \texttt{subset(dat, Var1 == "Low" | Var2 <= 5)} \\ Cleaning up & \texttt{rm()} & Removes object(s) from the Environment & \texttt{rm(object\_name)}; \texttt{rm(list = ls())} \\ \bottomrule \end{tabularx} \end{center} \end{small} \end{table} Some summary functions are presented in Table \ref{tab:summaries}. \begin{table}[htbp] \begin{small} \begin{center} \caption{Commonly used and useful summary functions.} \label{tab:summaries} \newcolumntype{R}{>{\raggedright\arraybackslash}X}% \begin{tabularx}{\textwidth}{R R R X } \toprule \textbf{Type} & \textbf{Function} & \textbf{What it does} & \textbf{Syntax} \\ \midrule Specifying variable in dataframe & \texttt{\$} & Gives the class (type of data structure) of the object & \texttt{dat\$blade\_length} \\ & \texttt{str()} & Lists variables in your object by name, their data type (continuous, factor) and an indication of the actual data & \texttt{str(dat)} \\ & \texttt{head()} & Gives first 6 rows of a dataframe, or number of rows (\texttt{n}) specified & \texttt{head(dat, 20)} \\ & \texttt{tail()} & Gives last 6 (or \texttt{n}) rows of a dataframe & \texttt{tail(dat, 10)} \\ & \texttt{names()} & Gives variable names & \texttt{names(dat)} \\ & \texttt{summary()} & Tabulates variables in dataframe and provides summary statistics & \texttt{summary(dat)} \\   & \texttt{with()} & Specify a dataframe & \texttt{with(dat, mean(blade\_length))} \\ Summary statistics & \texttt{mean()}, \texttt{sd()}, \texttt{range()}, \texttt{var()} & Calculates particular statistic for a variable. Use \texttt{na.rm = TRUE} if your data contain \texttt{NA}s & \emph{e.g.} \texttt{mean(dat\$blade\_length, na.rm = TRUE)} \\ & \texttt{length()} & Number of elements in a variable. Use \texttt{na.omit()} if your data contain \texttt{NA}s & \texttt{length(dat\$blade\_length)}; \texttt{length(na.omit(dat\$blade\_length))} \\ Data manipulation & \texttt{table()} & Frequency table by variables specified & \texttt{table(dat\$site, dat\$blade\_length)} \\ & \texttt{ftable()} & Flat frequency table useful for displaying multidimensional tables & \texttt{ftable(dat\$catvar1, dat\$catvar2, dat\$catvar3)} \\ Saving an object file & \texttt{write.csv()} & Save an object to a .csv file & \texttt{write.csv(sp\_by\_site, file = "Laminaria.csv", row.names = TRUE)} \\ \bottomrule \end{tabularx} \end{center} \end{small} \end{table}