16.2: Comparing Character Strings
- Page ID
- 85200
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Comparing strings is different than comparing numbering. Comparing strings requires specific functions. In this section, tf is a logical variable meaning true or false.
Consider two character string variables. Two common string comparison functions are:
tf = strcmp(str1, str2); % case sensitive
tf = strcmpi(str1, str2); % case insensitive
These functions look for a match between strings of the same length. The user can specify to compare just the first n characters.
Study the attached file: String_compare_demo.m
Create a Matlab script that does the following:
%% A. [1 pt] Create this array of names:
names = ['Alex';
'Gabe';
'Joan';
'John';
'Mary';
'Pete';
'Rosa';
'Tina']
%% B. [1 pt] Ask the user to enter a 4-letter name with this code:
name_in = input('Enter a 4-letter name: ','s');
%% C. [1 pt] Use length() to determine the length of the names array.
%% D. [5 pts] Write a for loop with loop index k to search for match of name_in
% to one of those in the names list. Use the following to find the match:
tf = strcmpi(name_in, names(k,:)); % case insensitive comparison
% When a match is found, display the index of that name in the list and break the loop
% Use disp() with num2str() to display the index with this code:
disp([name_in,' is number ',num2str(k),' in the list.'])
Extra Credit (2 pts) If a name is entered that is not in the list, figure out a way to send a message that the name is not in the list.
Are are 2 possible strategies:
Strategy A. Set a variable called valid_name = 0 before the loop.
Inside the loop, when a match is found, set valid_name = 1.
After the loop, if valid_name == 0, display a message that the name was not found.
Strategy B. Add an invalid name to the list, such as 'xxxx'. So, the length of the array will be 1 more than the number of valid names.
After the loop, if the loop index == the length of the array, than display a message that the name was not found.
- Answer
-
The answer is not shown here.
Other string functions are:
tf = strncmp(s1,s2,n): Compare first n characters of strings (case sensitive)
tf = strncmpi(s1,s2,n): Compare first n characters of strings (case insensitive)
tf = strfind(str,pat): Find strings within other strings
.