Is there a way here to write more efficient, more generic code?
As the value return doesn't change, do I need a switch here?
function result = whichValue(value)
switch value
case 'green_ok'
result = 'green&ok';
case 'green_ko'
result = 'green&ko';
case 'green_check'
result = 'green&check';
end
end
This seems like a poor way of doing things, but seems to work for your examples:
result=value
value(value=='_')='&'
How about using strsplit:
value_split = strsplit(value, '_');
result = [value_split{1}, '&', value_split{2}]
Related
I have a situation in MATLAB where I want to try to assign a struct field into a new variable, like this:
swimming = fish.carp;
BUT the field carp may or may not be defined. Is there a way to specify a default value in case carp is not a valid field? For example, in Perl I would write
my $swimming = $fish{carp} or my $swimming = 0;
where 0 is the default value and or specifies the action to be performed if the assignment fails. Seems like something similar should exist in MATLAB, but I can't seem to find any documentation of it. For the sake of code readability I'd rather not use an if statement or a try/catch block, if I can help it.
You can make your own function to handle this and keep the code rather clear. Something like:
swimming = get_struct(fish, 'carp', 0);
with
function v = get_struct(s, f, d)
if isfield(s, f)
v = s.(f); % Struct value
else
v = d; % Default value
end
Best,
From what I know, you can't do it in one line in MATLAB. MATLAB logical constructs require explicit if/else statements and can't do it in one line... like in Perl or Python.
What you can do is check to see if the fish structure contains the carp field. If it isn't, then you can set the default value to be 0.
Use isfield to help you do that. Therefore:
if isfield(fish, 'carp')
swimming = fish.carp;
else
swimming = 0;
end
Also, as what Ratbert said, you can put it into one line with commas... but again, you still need that if/else construct:
if isfield(fish,'carp'), swimming = fish.carp; else, swimming = 0;
Another possible workaround is to declare a custom function yourself that takes in a structure and a field, and allow it to return the value at the field, or 0.
function [out] = get_field(S, field)
if isfield(S, field)
out = S.(field);
else
out = 0;
end
Then, you can do this:
swimming = get_field(fish, 'carp');
swimming will either by 0, or fish.carp. This way, it doesn't sacrifice code readability, but you'll need to create a custom function to do what you want.
If you don't like to define a custom function in a separate function file - which is certainly a good option - you can define two anonymous functions at the beginning of your script instead.
helper = {#(s,f) 0, #(s,f) s.(f)}
getfieldOrDefault = #(s,f) helper{ isfield(s,f) + 1 }(s,f)
With the definition
fish.carp = 42
and the function calls
a = getfieldOrDefault(fish,'carp')
b = getfieldOrDefault(fish,'codfish')
you get for the first one
a = 42
and the previous defined default value for the second case
b = 0
L=1; Nx=51; PeriodicFlag=1; T=15; Nt=51;
spacedef='Pade6FirstDeriv'; casedef='LinearAdvection';
if (spacedef == 'Pade6FirstDeriv')
D1 = sparse(Pade6(Nx,dx,PeriodicFlag));
elseif (spacedef == 'Upwind3FirstDeriv')
D1 = sparse(Upwind3(Nx,dx,PeriodicFlag));
elseif (spacedef == 'Central4FirstDeriv')
D1 = sparse(Central4(Nx,dx,PeriodicFlag));
elseif (spacedef == 'Central2FirstDeriv')
D1 = sparse(Central2(Nx,dx,PeriodicFlag));
else
error(sprintf('Unknown spacedef = %s',spacedef));
end
In the above code, the if section is a small segment from a function I've constructed. I'm trying to get the function to know which methods to use based on my input (spacedef). Central2, Central4, Upwind3, and Pade6 are other functions I've written. The weird thing is that when spacedef =/= to 'Pade6FirstDeriv', I would get an error stating Error using ==, Matrix dimensions must agree. I've tried swapping the order of the if loop (by placing Central4, Central2, Pade6, and Upwind3 in the first line of the loop), and it seems like only the top line of the loop will work (the elseifs are not working). I'd greatly appreciate it if anybody can help me out. Thanks!
As has been noted in the comments, this is a common error when people first start comparing strings in MATLAB, and strcmp or strcmpi is generally the solution.
However, one solution the questions links in the comments don't present, and a solution I think looks much nicer, is the switch statement:
switch (spacedef)
case('Pade6FirstDeriv')
D1 = sparse(Pade6(Nx,dx,PeriodicFlag));
case('Upwind3FirstDeriv')
D1 = sparse(Upwind3(Nx,dx,PeriodicFlag));
case('Central4FirstDeriv')
D1 = sparse(Central4(Nx,dx,PeriodicFlag));
case('Central2FirstDeriv')
D1 = sparse(Central2(Nx,dx,PeriodicFlag));
otherwise
error(sprintf('Unknown spacedef = %s',spacedef));
end
Note: if I expect others to use my code with string comparisons, I usually lower the input such that the comparison is case-insensitive, although I have not done that here.
function myFunc = executeCmdByKind(var1,kind)
switch kind
case 'open'
cmdToExecute = [''var1 '','' locationIs '',''clear''];
case 'close'
cmdToExecute = [''var1 '','' locationIs '',''delete''];
case 'move'
cmdToExecute = [''var1 '','' locationIs '',''move''];
end
a = system(cmdToExecute);
end
My question is : is there a better way "optimal" to write this code as I call the same cmdToExecute only the latest arg changes
Thanks,
Your syntax makes no sense to me, but I'll stick with it. You could streamline your code like this I guess:
function myFunc = executeCmdByKind(var1,kind)
switch kind
case 'open'
last = ''clear'';
case 'close'
last = ''delete'';
case 'move'
last = ''move'';
end
cmdToExecute = [''var1 '','' locationIs '', last];
There are, as always, several ways of doing it. I'd do it like the following:
function myFunc = executeCmdByKind(var1,kind)
a = {'open', 'close', 'move'};
b = {'clear', 'delete', 'move'};
logi = ismember(a, kind);
cmdToExecute = [var1, locationIs, b{logi}];
That's not the nicest code, but it's short, if you want that ;-)
First I look via kind which index it has in the vector a and after retreiving the index, I can then select the corresponding element from b :-)
Edit: Short and it's easily expandable in the future with more elements :-)
I am aware many of you will think this should be easily solvable. However, I have no clue about MATLAB.
Here goes my problem: when trying to execute the following example in the Command Window through the command
getLogReturnExcel('ALL.xls', {'ALL'}, 37000, 38000)
the cell-type error appears for this function. From what I understand however, when using {} the function should be grabbing the type inside {} (String in this case?) instead of the cell itself, which would be being grabbed if we were to use (), so there should be no error? Or is there something much more elementary that I might be overseeing? Thanks in advance for every bit of help; as you can tell I very much need it.
Cheers,
Ben
Here goes the function getLogReturnExcel:
function [logreturn, datearray] = getLogReturnExcel( datafilename, ticker, begindate, enddate )
[aanumber, aatext] = xlsread(datafilename);
aaticker = aatext(:,1);
aadate = aanumber(:,2);
aaret = zeros(length(aaticker),1);
aaret(1,1) = 0;
for i = 2:length(aaret)
aaret(i,1) = ln(aanumber(i,3))-ln(aanumber(i-1,3));
end
aadate = aadate(strcmp(aaticker,ticker));
aaret = aaret(strcmp(aaticker,ticker));
logreturn = aaret(aadate>=begindate & aadate<=enddate);
datearray = aadate(aadate>=begindate & aadate<=enddate);
return
The file 'ALL.xls' contains 3 columns, one with strings (the acronym for stocks) and two with numbers (I'm assuming double), one for the date in Excel-format and one with each day's stock standing.
The string can be obtained by using:
ticker{:}
or else the comparison in the lines
aadate = aadate(strcmp(aaticker,ticker));
aaret = aaret(strcmp(aaticker,ticker));
will be between strings and cell array.
Here is some documentation to access elements of a cell array.
In Matlab, I've got a function that is called after some special points are found on an image. Depending on how the nearby pixels of that "special point" are, the function must return a structure with many parameters or return nothing.
Is it possible to have a function that by deafult will return something but, in some cases, nothing should be returned? How that "return nothing"'s code should be like? Thank you.
One common trick in matlab is to use the empty matrix [] to indicate nothing. You could write your function something like (untested code):
function result = analyze(image, special_point)
% your code here
if pixels_are_ok
result.a = 1;
result.b = 2;
else
result = [];
end
If you call this function from your other code, you can use isempty to see if you got a result or not:
result = analyze(image, special_point)
if isempty(result)
display('did not find anything')
else
display('found some interesting results')
display(result)
end