[programming] add box on string type

programming/lecture/programming.tex

@@ -176,11 +176,12 @@ As mentioned above, the data type associated with a variable defines how the sto
   part.
 \item \enterm{logical}: Boolean values that can be evaluated to
   \code{true} or \code{false}.
-\item \enterm{character}: ASCII characters.
+\item \enterm{character}: Unicode characters.
+\item \enterm{string}: Strings of unicode characters, i.e. text. 
 \end{itemize}
 There is a variety of numeric data types that require different
 amounts of memory and have different ranges of values that can be
-represented (table~\ref{dtypestab}).
+represented (table~\ref{dtypestab}). There are also more advanced data types which will not be used in this chapter but see box~\ref{box:advanced_dtypes} and box about strings \ref{box:strings}.
 
 \begin{table}[t]
   \centering
@@ -1156,7 +1157,7 @@ segment of data of a certain time span (the stimulus was on,
   \end{itemize}
 \end{exercise}
 
-\begin{ibox}[ht]{\label{advancedtypesbox}Advanced data types}
+\begin{ibox}[!ht]{\label{advancedtypesbox}Advanced data types}
   Thoughout this script and the exercises we will limit ourselves to
   the basic data types introduced above (int, double, char, scalars,
   vectors, matrices and strings). There are, however, \matlab{}-
@@ -1212,6 +1213,50 @@ ans =
 
 \end{ibox}
 
+\begin{ibox}[!ht]{\label{box:string_dtype}The \enterm[string]{string} data type}
+    With release 2017a \matlab{} introduced the string data type which offers more convenience for handling text. A string scalar is created using double quotes: \varcode{s = "Hello world!";}.
+    The string object \varcode{s} now offers several methods to work on the stored information. Some of the most commonly used methods are listed below. Refer to the documentation for complete descriptions.
+    \begin{enumerate}
+        \item \varcode{append} -- appends another string to the string and returns the new string. As with the other functions the original is not affected.\vspace{-0.5em}
+        \item \varcode{contains} -- searches the string for the occurence of a another string, which is passed as an argument. Returns a logical that is true if the pattern was found.\vspace{-0.5em} 
+        \item \varcode{split} -- splits the string into substrings. By default a blank is used as delimiter. You can pass any other string as an argument to spilt the string at each occurence of the passed pattern. Returns a vector of substrings.\vspace{-0.5em}
+        \item \varcode{join} --  The opposite of spilt. \varcode{join} takes a vector of strings and concatenates them to a single string. By default a blank is used as delimiter.\vspace{-0.5em}
+        \item \varcode{lower} -- returns a version of the string in which all characters are lower case. This is particularly useful when one compares user input or string arguments in a function in an case insensitive way.\vspace{-0.5em}
+        \item \varcode{upper} -- as above but all characters are converted to upper case.        
+    \end{enumerate} 
+    \paragraph{Example:}
+    A dataset is recorded on a specific recording date using an experimental subject and applying certain stimulus conditions. The recorded data should be stored in a file that contains this information separated by undersores.
+
+    \begin{lstlisting}[basicstyle=\ttfamily\scriptsize, caption={Using \varcode{join} to combine strings.}, label=usingjoin]
+date = "2020-12-24";
+subject = "subjectA";
+condition = "control";
+file_extension = ".dat";
+
+filename = join([date, subject, condition], "_");
+filename = filename.append(file_extension)
+        
+disp(filename)
+
+ans = 
+     "2020-12-24_subjectA_control.dat"
+    \end{lstlisting}
+
+    When reading the dataset during the analysis, we may want to extract the stimulus condtion or the subject name.
+    
+    \begin{lstlisting}[basicstyle=\ttfamily\scriptsize, caption={Using \varcode{split} to cut a string at a delimiter.}, label=usingsplit]
+disp(filename)
+ans = 
+    "2020-12-24_subjectA_control.dat"
+    
+filename = filename.erase(".dat");  % remove file extension
+string_parts = filename.split("_");  % split at the underscore
+% string_parts is a vector of the substrings
+date = string_parts(1);
+subject = string_parts(2);
+condition = string_parts(3);
+    \end{lstlisting}
+\end{ibox}
 \section{Control flow}\label{controlstructsec}
 
 Generally, a program is executed line by line from top to