Please write a Matlab function to find the first vowel in a word, and test the program using your name as the input.
The function header is function v = findfirstvowel (word)
My work is :
function v = findfirstvowel (word)
vow = 'aeiouAEIOU';
for i=1:size(word)
for j=1:10
if word(i)==vow(j)
v=word(i);
break;
end
end
end
I don't know why but I didn't work
The break only breaks out of the innermost for loop.
From the documentation:
In nested loops, break exits only from the loop in which it occurs. Control passes to the statement that follows the end of that loop.
If you want to exit the function, you'd want to use return instead.
function v = findfirstvowel (word)
vow = 'aeiouAEIOU';
for i=1:size(word)
for j=1:10
if word(i)==vow(j)
v=word(i);
return;
end
end
end
Instead of the double for loop, you'd be much better off using something like ismember to check to find the vowels and use find to return the index of the first one. Also you can convert the word to lowercase and only compare to 'aeiou'.
function v = findfirstvowel (word)
isvowel = ismember(lower(word), 'aeiou');
v = word(find(isvowel, 1, 'first'));
end
If you wanted the other vowels using this approach you could do the following.
isvowel = ismember(lower(word), 'aeiou');
vowels = word(isvowel);
first_vowel = vowels(1);
second_vowel = vowels(2);
Related
I have a segment of code where a composition of nested loops needs to be run at various times; however, each time the operations within the nested loops are different. Is there a way to make the outer portion (loop composition) somehow a functional piece, so that the internal operations are variable. For example, below, two code blocks are shown which both use the same loop introduction, but have different purposes. According to the principle of DRY, how can I improve this, so as not to need to repeat myself each time a similar loop needs to be used?
% BLOCK 1
for a = 0:max(aVec)
for p = find(aVec'==a)
iDval = iDauVec{p};
switch numel(iDval)
case 2
r = rEqVec(iDval);
qVec(iDval(1)) = qVec(p) * (r(2)^0.5 / (r(1)^0.5 + r(2)^0.5));
qVec(iDval(2)) = qVec(p) - qVec(iDval(1));
case 1
qVec(iDval) = qVec(p);
end
end
end
% BLOCK 2
for gen = 0:max(genVec)-1
for p = find(genVec'==gen)
iDval = iDauVec{p};
QinitVec(iDval) = QinitVec(p)/numel(iDval);
end
end
You can write your loop structure as a function, which takes a function handle as one of its inputs. Within the loop structure, you can call this function to carry out your operation.
It looks as if the code inside the loop needs the values of p and iDval, and needs to assign to different elements of a vector variable in the workspace. In that case a suitable function definition might be something like this:
function vec = applyFunctionInLoop(aVec, vec, iDauVec, funcToApply)
for a = 0:max(aVec)
for p = find(aVec'==a)
iDval = iDauVec{p};
vec = funcToApply(vec, iDval, p);
end
end
end
You would need to put the code for each different operation you want to carry out in this way into a function with suitable input and output arguments:
function qvec = myFunc1(qVec, iDval, p)
switch numel(iDval)
case 2
r = rEqVec(iDval); % see note
qVec(iDval(1)) = qVec(p) * (r(2)^0.5 / (r(1)^0.5 + r(2)^0.5));
qVec(iDval(2)) = qVec(p) - qVec(iDval(1));
case 1
qVec(iDval) = qVec(p);
end
end
function v = myFunc2(v, ix, q)
v(ix) = v(q)/numel(ix);
end
Now you can use your loop structure to apply each function:
qvec = applyFunctionInLoop(aVec, qVec, iDauVec, myFunc1);
QinitVec = applyFunctionInLoop(aVec, QinitVec, iDauVec, myFunc2);
and so on.
In most of the answer I've kept to the same variable names you used in your question, but in the definition of myFunc2 I've changed the names to emphasise that these variables are local to the function definition - the function is not operating on the variables you passed in to it, but on the values of those variables, which is why we have to pass the final value of the vector out again.
Note that if you want to use the values of other variables in your functions, such as rEqVec in myFunc1, you need to think about whether those variables will be available in the function's workspace. I recommend reading these help pages on the Mathworks site:
Share Data Between Workspaces
Dynamic Function Creation with Anonymous and Nested Functions
Is there a way to have one function that can return two different variables, but only one at a time AND knowing which one is returned in the function call?
example:
I have the following function in which only one of the outputs is valid (the other one would be [])
function [a,b] = AlternatingOutput (input)
if input == 1
return ONLY A
else
return ONLY B
end
end
and i call it in a script
[a,b] = AlternatingOutput (input)
i want a way to say the following (pseudocode):
if (function outputs a)
[a,~] = AlternatingOutput(input)
elseif (function outputs b)
[~,b] = AlternatingOutput(input)
end
the script is run in a loop, and later i need the newest Valid values for a and b, so i cannot overwrite one of the two with []
I do understand that I could just write a function that checks which variable will be output, but I was wondering if there is a more elegant way.
I hope I have made my question clear, and I hope someone can answer me :)
There is no way to tell if an output argument is actually used. You may check the number of output arguments using nargout and it would allow to distinguish between [a] = AlternatingOutput(input) and [~,b] = AlternatingOutput(input)
I don't know the full context of your problem, but maybe you can put all your variables into a struct? Simply pass this struct everytime you call the function and let it decide which variables to manipulate. (This might be slow in some programming languages, but not in matlab).
How about retuning a cell?
function [ ab ] = testfun( input )
if input
ab={'ax'};
else
ab={2};
end
end
No worries about what is in the cell.
thb you could return what ever you want, Matlab does not check the type anyways
If only one of the outputs from the function AlternatingOutput is valid, then you only need to return one output:
function [X] = AlternatingOutput(input)
if input == 1
X = A;
else
X = B;
end
end
To allocate the retured value to either a or b in the loop, put them into a cell:
C = {AlternatingOutput(1), AlternatingOutput(2)};
and then use input to determine which value is change. If input is either 1 or 2 you can just do
for counter = ...
input = mod(input,2)+1;
C{input}=AlternatingOutput(input);
end
If your function doesn't mind accepting more input variables, why not pass a and b as input:
function [a,b] = AlternatingOutput(a,b,input)
if input == 1
a = new_value_for_a;
% b retains its former value
else
% a retains its former value
b = new_value_for_b;
end
end
Then it can be easily called from your script in a loop:
for i= ...
[a,b] = AlternatingOutput(a,b,input);
...
...
end
I am working on implementing queue data structures using cell arrays in Matlab. I am trying to write functions to advance the queue by one, as well as search the queue for a specific item. At the moment the function looks like this (car types are the example data).
function q = createQueue()
q={};
q = enqueue(q,'Hilux');
q = enqueue(q,'E-Type');
q = enqueue(q,'Beetle');
q = enqueue(q,'Enzo');
q = enqueue(q,'Boxter');
q = dequeue(q)
q = searchQueue(q,'Boxter')
end
% Adds an item to the end of the queue. Returns the new queue.
function q = enqueue(q,item)
q{end+1} = item;
end
function [q item] = dequeue(q)
q{1} = {};
q{1} = q{2};
q{2} = q{3};
q{3} = q{4};
q{4} = q{5};
q{5} = {};
end
function answer = searchQueue(q, item)
for i = 1:length(q)
if q{i} == item
answer = fprintf('FOUND AT INDEX %d',i);
break
else
disp('-1')
end
end
end
Currently, the dequeue function leaves an empty cell, rather than removing the cell entirely. Is this able to be avoided? The searchQueue function also returns an error, and i am lost as to why. Thanks
Here's a rough first cut at it using matlab's object oriented capabilities. The reason for creating a class is to get reference semantics from the handle type, which allows for the dequeue/enqueue functions to modify the cell array directly, removing the need for reassignment.
I believe the code example below answers your main question about how to dequeue without leaving an empty cell (could be used without the OOP approach to the same effect).
To answer your question about what's wrong with your search: 1) the comparison q{i} == item gives you problems because == compares characters (which fails if there is a string size mismatch) whereas you wanted to use isequal(); 2) you wanted sprintf rather than fprintf; and 3) while not strictly wrong, the else in your loop happens on every item that doesn't match, which is probably not what you wanted.
classdef Queue < handle
properties
data = {}
end
methods
function q = Queue()
% TODO: do something in constructor if desired
end
function item = dequeue(q)
% TODO: bounds check
item = q.data(1);
q.data = q.data(2:end);
end
function enqueue(q,item)
q.data{end+1} = item;
end
function answer = search(q, item)
% TODO: check for multiple occurrences
answer = 'NOT FOUND';
for i = 1:length(q.data)
if isequal(q.data{i},item)
answer = sprintf('FOUND AT INDEX %d',i);
break
end
end
end
end
end
I have created a matrix with row 1 full of strings and 4 other rows with numbers. They are created in a handle class with the object "Projekter".
So in the object "Projekter" row 1, the first value is blank, but the second value is 'Ole'. So I know that 'Ole' is in (1,2). x is the name/string I want to search for, which in this case is 'Ole'.
As you see below it should search row 1 from column 2 untill the last name/string and if i = 'Ole', it should bring me the value 2 because " i " should be equal 2.
A is just a controller if the function works, but at this point it doesn't.
The error it gives is "Undefined function 'eq' for input arguments of type 'cell'."
How do I fix this so it return the " i " value when the statement is correct?
Thank you in advance!
function number(obj,x)
A = [];
for i = 2:size(obj.Projekter,2)
if obj.Projekter(1,i)==x
A = A + 1;
end
end
disp(A)
end
Maybe you have to index the cell content:
your_cell = {'a_string'};
your_string = your_cell{1};
function [returnValue] = number(obj,x)
for i = 2:size(obj.Projekter,2)
if obj.Projekter{1,i}==x
returnValue = i;
return;
end
end
end
Note the change from obj.Projekter(1,i)==x to obj.Projekter{1,i}==x (use curly braces instead of parens). I have then specified that returnValue will hold the value that should be returned by doing function [returnValue] = number(obj,x). We then set returnValue equal to i and return from the function when the condition of the if statement is true.
As suggested in the comments, it is probably better to do:
function [returnValue] = number(obj, x)
returnValue = find(strcmp(x, obj.Projekter) == 1);
strcmp(x, obj.Projektor) will give you an array the length of obj.Projekter with 1's wherever the strings match, and 0's where they don't, you can then find the indices that are set to 1. This has the added benefit of
not using a loop so it's faster
Giving you every occurrence of a match, not just the first one.
Aside from parsing the function file, is there a way to get the names of the input and output arguments to a function in matlab?
For example, given the following function file:
divide.m
function [value, remain] = divide(left, right)
value = floor(left / right);
remain = left / right - value;
end
From outside the function, I want to get an array of output arguments, here: ['value', 'remain'], and similarly for the input arguments: ['left', 'right'].
Is there an easy way to do this in matlab? Matlab usually seems to support reflection pretty well.
EDIT Background:
The aim of this is to present the function parameters in a window for the user to enter. I'm writing a kind of signal processing program, and functions to perform operations on these signals are stored in a subfolder. I already have a list and the names of each function from which the user can select, but some functions require additional arguments (e.g. a smooth function might take window size as a parameter).
At the moment, I can add a new function to the subfolder which the program will find, and the user can select it to perform an operation. What I'm missing is for the user to specify the input and output parameters, and here I've hit the hurdle here in that I can't find the names of the functions.
MATLAB offers a way to get information about class metadata (using the meta package), however this is only available for OOP classes not regular functions.
One trick is to write a class definition on the fly, which contain the source of the function you would like to process, and let MATLAB deal with the parsing of the source code (which can be tricky as you'd imagine: function definition line spans multiple lines, comments before the actual definition, etc...)
So the temporary file created in your case would look like:
classdef SomeTempClassName
methods
function [value, remain] = divide(left, right)
%# ...
end
end
end
which can be then passed to meta.class.fromName to parse for metadata...
Here is a quick-and-dirty implementation of this hack:
function [inputNames,outputNames] = getArgNames(functionFile)
%# get some random file name
fname = tempname;
[~,fname] = fileparts(fname);
%# read input function content as string
str = fileread(which(functionFile));
%# build a class containing that function source, and write it to file
fid = fopen([fname '.m'], 'w');
fprintf(fid, 'classdef %s; methods;\n %s\n end; end', fname, str);
fclose(fid);
%# terminating function definition with an end statement is not
%# always required, but now becomes required with classdef
missingEndErrMsg = 'An END might be missing, possibly matching CLASSDEF.';
c = checkcode([fname '.m']); %# run mlint code analyzer on file
if ismember(missingEndErrMsg,{c.message})
% append "end" keyword to class file
str = fileread([fname '.m']);
fid = fopen([fname '.m'], 'w');
fprintf(fid, '%s \n end', str);
fclose(fid);
end
%# refresh path to force MATLAB to detect new class
rehash
%# introspection (deal with cases of nested/sub-function)
m = meta.class.fromName(fname);
idx = find(ismember({m.MethodList.Name},functionFile));
inputNames = m.MethodList(idx).InputNames;
outputNames = m.MethodList(idx).OutputNames;
%# delete temp file when done
delete([fname '.m'])
end
and simply run as:
>> [in,out] = getArgNames('divide')
in =
'left'
'right'
out =
'value'
'remain'
If your problem is limited to the simple case where you want to parse the function declaration line of a primary function in a file (i.e. you won't be dealing with local functions, nested functions, or anonymous functions), then you can extract the input and output argument names as they appear in the file using some standard string operations and regular expressions. The function declaration line has a standard format, but you have to account for a few variations due to:
Varying amounts of white space or blank lines,
The presence of single-line or block comments, and
Having the declaration broken up on more than one line.
(It turns out that accounting for a block comment was the trickiest part...)
I've put together a function get_arg_names that will handle all the above. If you give it a path to the function file, it will return two cell arrays containing your input and output parameter strings (or empty cell arrays if there are none). Note that functions with variable input or output lists will simply list 'varargin' or 'varargout', respectively, for the variable names. Here's the function:
function [inputNames, outputNames] = get_arg_names(filePath)
% Open the file:
fid = fopen(filePath);
% Skip leading comments and empty lines:
defLine = '';
while all(isspace(defLine))
defLine = strip_comments(fgets(fid));
end
% Collect all lines if the definition is on multiple lines:
index = strfind(defLine, '...');
while ~isempty(index)
defLine = [defLine(1:index-1) strip_comments(fgets(fid))];
index = strfind(defLine, '...');
end
% Close the file:
fclose(fid);
% Create the regular expression to match:
matchStr = '\s*function\s+';
if any(defLine == '=')
matchStr = strcat(matchStr, '\[?(?<outArgs>[\w, ]*)\]?\s*=\s*');
end
matchStr = strcat(matchStr, '\w+\s*\(?(?<inArgs>[\w, ]*)\)?');
% Parse the definition line (case insensitive):
argStruct = regexpi(defLine, matchStr, 'names');
% Format the input argument names:
if isfield(argStruct, 'inArgs') && ~isempty(argStruct.inArgs)
inputNames = strtrim(textscan(argStruct.inArgs, '%s', ...
'Delimiter', ','));
else
inputNames = {};
end
% Format the output argument names:
if isfield(argStruct, 'outArgs') && ~isempty(argStruct.outArgs)
outputNames = strtrim(textscan(argStruct.outArgs, '%s', ...
'Delimiter', ','));
else
outputNames = {};
end
% Nested functions:
function str = strip_comments(str)
if strcmp(strtrim(str), '%{')
strip_comment_block;
str = strip_comments(fgets(fid));
else
str = strtok([' ' str], '%');
end
end
function strip_comment_block
str = strtrim(fgets(fid));
while ~strcmp(str, '%}')
if strcmp(str, '%{')
strip_comment_block;
end
str = strtrim(fgets(fid));
end
end
end
This is going to be very hard (read: impossible) to do for general functions (think of things like varargin, etc). Also, in general, relying on variable names as a form of documentation might be... not what you want. I'm going to suggest a different approach.
Since you control the program, what about specifying each module not just with the m-file, but also with a table entry with extra information. You could document the extra parameters, the function itself, notate when options are booleans and present them as checkboxes, etc.
Now, where to put this? I would suggest to have the main m-file function return the structure, as sort of a module loading step, with a function handle that points to the subfunction (or nested function) that does the real work. This preserves the single-file setup that I'm sure you want to keep, and makes for a much more configurable setup for your modules.
function module = divide_load()
module.fn = #my_divide;
module.name = 'Divide';
module.description = 'Divide two signals';
module.param(1).name = 'left';
module.param(1).description = 'left signal';
module.param(1).required_shape = 'columnvector';
% Etc, etc.
function [value, remain] = my_divide(left, right)
value = floor(left / right);
remain = left / right - value;
end
end
When you can't get information from a programming langauge about its contents (e.g., "reflection"), you have to step outside the language.
Another poster suggested "regular expressions", which always fail when applied to parsing real programs because regexps cannot parse context free langauges.
To do this reliably, you need a real M language parser, that will give you access to the parse tree. Then this is fairly easy.
Our DMS Software Reengineering Toolkit has an M language parser available for it, and could do this.
Have you considered using map containers?
You can write your functions along these lines . . .
function [outMAP] = divide(inMAP)
outMAP = containers.Map();
outMAP('value') = floor(inMAP('left') / inMAP('right'));
outMAP('remain') = inMAP('left') / inMAP('right') - outMAP('value');
end
...and call them like this ...
inMAP = containers.Map({'left', 'right'}, {4, 5});
outMAP = divide(inMAP);
...and then simply examine tha variable names using the following syntax...
>> keys(inMAP)
ans =
'left' 'right'
inputname(argnum) http://www.mathworks.com/help/techdoc/ref/inputname.html .