Working on class slides

Class8/Class_Examples/apply.r

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+DAT <- 1:8
+?apply
+apply(DAT,mean)
+?mapply
+x <- as.data.frame(cbind(x1 = c(3,NA,12,7), x2 = c(4:1, 2:5)) )
+dimnames(x)[[1]] <- letters[1:8]
+apply(x, 2, mean, trim = .2,na.rm=TRUE)
+?mean

Class8/Slides/Joins.tex

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+\documentclass{beamer}
+\usepackage{graphicx}
+\usepackage{multicol}
+\usepackage{hyperref}
+\usepackage{verbatim}
+\usepackage{lipsum} % for placeholder text
+\graphicspath{{pdf_images/}}
+
+
+\title{ECON 4530/5530 \\ Computational Economics}
+\subtitle{Joining data and Data Transformation}
+\author{Alex Gebben}
+
+\begin{document}
+
+% Title Slide
+\begin{frame}
+  \titlepage
+\end{frame}
+%%%%%%%%%%%%%%%%%%
+\begin{frame}{Joining Data}
+\begin{itemize}
+  \item Real-world data often comes in multiple tables.
+  \item Joins combine related data based on common keys.
+  \item \texttt{dplyr} provides intuitive functions for joining.
+\end{itemize}
+\end{frame}
+
+% Slide 2
+\begin{frame}{Types of Joins}
+\begin{itemize}
+  \item \texttt{left\_join()} – keep all rows from left table
+  \item \texttt{right\_join()} – keep all rows from right table
+  \item \texttt{inner\_join()} – keep only matching rows
+  \item \texttt{full\_join()} – keep all rows from both tables
+\end{itemize}
+\end{frame}
+
+% Slide 3
+\begin{frame}{left\_join()}
+\texttt{left\_join(df1, df2, by = "id")}
+\newline
+OR
+\newline
+\onslide<2->{\texttt{df1 \%>\% left\_join(df2)}}
+\begin{itemize}
+	\onslide<3->{ \item Keeps all rows from the left table.}
+	\onslide<4->{ \item Adds matching rows from the right table.}
+	\onslide<5->{ \item Missing matches are filled with \texttt{NA}.}
+\end{itemize}
+\end{frame}
+
+% Slide 4
+\begin{frame}{right\_join()}
+
+\texttt{right\_join(df1, df2, by = "id")}
+\newline
+OR
+\newline
+\onslide<2->{\texttt{df2 \%>\% left\_join(df1)}}
+\onslide<3->{
+\begin{itemize}
+  \item Keeps all rows from the right table.
+  \item Adds matching rows from the left table.
+\end{itemize}
+}
+\end{frame}
+
+% Slide 5
+\begin{frame}{inner\_join()}
+\texttt{inner\_join(df1, df2, by = "id")}
+\newline
+OR
+\newline
+\texttt{df1 \%>\% inner\_join(df2, by = "id")}
+\begin{itemize}
+  \item Keeps only rows with matching keys in both tables.
+  \item Most commonly used for filtering to shared data.
+\end{itemize}
+\end{frame}
+
+% Slide 6
+\begin{frame}{full\_join()}
+\texttt{full\_join(df1, df2, by = "id")}
+\newline
+OR
+\newline
+\texttt{df1 \%>\% full\_join(df2, by = "id")}
+
+\begin{itemize}
+  \item Keeps all rows from both tables.
+  \item Missing matches are filled with \texttt{NA}.
+\end{itemize}
+\end{frame}
+\begin{frame}{Common Issues}
+\begin{itemize}
+  \item Mismatched column names 
+  \item Duplicate keys – can lead to unexpected row duplication
+  \item Data types must match, both keys should be character or numeric
+  \item Missing value joins will introduce \texttt{NA}s
+\end{itemize}
+
+\end{frame}
+
+\begin{frame}[plain]
+		\includegraphics[width=\textwidth]{venn.png}
+\end{frame}
+
+\begin{frame}[plain]
+	\begin{columns}
+		\begin{column}{0.5\textwidth}
+		\includegraphics[width=\textwidth]{1_join}
+		\end{column}
+		\begin{column}{0.5\textwidth}
+		\includegraphics[width=\textwidth]{2_join}
+		\end{column}
+	\end{columns}
+\end{frame}
+
+\begin{frame}[plain]
+		\includegraphics[width=\textwidth]{3_join}
+\end{frame}
+\begin{frame}[plain]
+		\includegraphics[width=\textwidth]{full.png}
+\end{frame}
+\begin{frame}[plain]
+		\includegraphics[width=\textwidth]{left.png}
+\end{frame}
+\begin{frame}[plain]
+		\includegraphics[width=\textwidth]{right.png}
+\end{frame}
+
+
+
+
+% Slide 7
+\begin{frame}[plain]
+		\includegraphics[width=\textwidth]{match-types.png}
+\end{frame}
+\begin{frame}{Checking with Anti-Joins}
+		\includegraphics[width=\textwidth]{anti.png}
+\end{frame}
+\begin{frame}{Checking with Anti-Joins}
+		\includegraphics[width=\textwidth]{anti.png}
+\end{frame}
+\begin{frame}{Filtering with semi-joins}
+		\includegraphics[width=\textwidth]{semi.png}
+\end{frame}
+\begin{frame}{Other non-equa joins}
+		\includegraphics[width=\textwidth]{gte}
+\end{frame}
+
+% Slide 8
+\begin{frame}{Best Practices}
+\begin{itemize}
+  \item Inspect keys before joining: \texttt{unique()}
+  \item Use \texttt{anti\_join()} to find unmatched rows
+  \item Validate results with \texttt{summary()} and \texttt{count()}
+\end{itemize}
+\end{frame}
+
+% Slide 9
+\begin{frame}{Class Exercise}
+\begin{itemize}
+  \item Joins are essential for combining data.
+  \item Choose the right join based on your goal.
+  \item Always check for common issues before and after joining.
+\end{itemize}
+\end{frame}
+
+\end{document}