I'm designing a function that takes as argument one structure and any number of flags. The function will contain a couple of ifs checking whether a specific flag is set.
What is the neatest way to achieve this? I was thinking about passing the flags as separate string arguments. Is there a neater solution?
I would do it like using varargin and ismember:
function foo(arg1,arg2,varargin)
flag1=ismember('flag1',varargin);
flag2=ismember('flag2',varargin);
flag3=ismember('flag3',varargin);
And you can call the function like that:
foo(a1,a2,'flag3','flag1')
This will activate flag1 and flag3.
Pass in a struct of flags:
options = struct(...
'Flag1', true, ...
'Flag2', true, ...
'MySpecifFlag', false ...
);
Foo(st, options);
To get a list of all the flags that were explicitly set by the user, use fieldnames:
passedOptions = fieldnames(options);
This returns a cell array whose elements are strings - these strings are the flags set by the user; the ith element of the array is the ith flag set by the user.
Access the value of each flag that was set:
options.(passedOptions{i}) %# gets the value of the flag corresponding to passedOptions{i}
Probably you can pass varargin -
The even will be names of the flags and the odd their values (except the first)
function Foo(st, varargin)
end
Then pass values like this:
Foo(st, 'Flag1', true, 'Flag2', false)
Foo(st, 'Flag3', true, 'MyFlag2', false,'MySpecialFlag',false)
Foo(st)
To access the variable arguments use
varargin{2}, varargin{3},
etc..
To check whether a specific flag was passed, do
flagNames = varargin{2:end};
ismember('MyFlag',flagNames )
You can pass the flags as a string with 0s and 1s. The order can be fixed or you can also pass a cell array of flag names.
flagstr = '101'; %# string passed as argument
flaglog = flagstr=='1'; %# logical vector, can be accessed as flaglog(i)
fname = {'flag1','flag2','flag3'}; %# flag names, can be passed as argument or defined in the function
fvalue = num2cell(flaglog); %# create cell array
flags = cell2struct(fvalue, fname, 2); %# create a structure, so you can access a flag with flags.flag1
You need to take care to match the length of fvalue and fnames. if they are different you can either generate an error or somehow correct it (remove the extra flags or fill the absent by default value).
varargin is the way to go for parsing a variable number of arbitrary input arguments. If you want somemore control over the calling syntax of the function (i.e. optional/required arguments) then I suggest looking into Matlab's input parser.
Related
I've been stuck with this for a while and I couldn't find something similar asked previously (or I have failed in doing so)
My situation is fairly simple: I have a cell array of objects. They are all the same object and I have a get function for this kind of object which is: get (obj, attr), where obj is the object in question and attr is a integer from 1-6. Depending on the number the get function returns the corresponding attribute.
I would like to obtain all of my "position" attributes from all my objects which are in the corresponding cell array (this would be attr = 2). I know that cellfun performs a function on all cells, but the question is, how do I use my get function here for all my objects, taking into account that the function is get (obj, attr) ?
Thanks in advance
Firstly, by using get as a custom function you are shadowing the built-in get function - this is bad practise!
With this in mind, and to avoid confusion with the built-in get function which has similar syntax, I'm going to use getattr as a stand-in for your custom function which accpets an object and an integer 1 to 6.
pos = cellfun( #(obj) getattr( obj, 2 ), myCellOfObjects, 'uni', 0 );
By specifying 'uni', 0, the output doesn't have to be scalar and will be put into a cell array. This is useful when, for example, you have a multi-element array for your position.
This is equivalent to the following loop:
pos = cell( numel(myCellOfObjects), 1 );
for ii = 1:numel(pos)
pos{ii} = getattr( myCellOfObjects{ii}, 2 );
end
If ever in doubt about cellfun or arrayfun, just write a loop first - they are essentially the same but more concise.
There is a trick to this some are unaware of: you can pass multiple arguments to cellfun like this:
cellfun(#(obj,attr) get(obj,attr), {obj1,obj2},{attr1,attr2},'uni',0)
if you want to get one attribute of the cellarray (instead of providing an attribute for every object in the cellarray), then you can simply use this
cellfun(#(x) getattr(x,attr),obj,'uni',0)
put into anonymous function for convenience:
get_attr = #(obj,attr) cellfun(#(x) getattr(x,attr),obj,'uni',0)
%use:
get_attr(obj_in_cellarray,'myattribute')
%returns cell array of object attributes
I haven't run any of these functions since you didn't provide any example data / code. Please test and feedback.
For (MEX) function calls it would be really nice to pass several properties of one object at once. Instead of foo(myObj.propA, myObj.propB) I want something like foo(myObj.[propA,propB].
Is this even possible?
With structs it is possible to use the getfield() function to get the data from more than one field, e.g.:
getfield(myStruct, {index}, {'fieldA', 'fieldB'})
But unfortunately, the following attempt to get more than one property from an object results in an error (Index exceeds matrix dimensions):
getfield(myObj, {index}, {'propA', 'propB'})
Maybe the only possibility is to write a function which returns several output arguments:
[varargout] = getProps(object,propnames)
for p=1:numel(propnames)
varargout{p} = object.(propnames{p});
end
But if I call another function with that function as input, e.g. sum(getProps(myObj,propnames)) only the first output argument of getProps is passed and I fall into despair. Is there any other way?
For an object, you'd use get, not getfield (or dynamic access in a loop like you showed).
>> h = figure;
>> get(h,{'Position','Renderer'})
ans =
[1x4 double] 'opengl'
This doesn't work for all objects, but for MATLAB graphics objects it does work. To deal with any class, you can use your function, but with a custom cell output instead of varargout:
function C = getProps(object,propnames)
for p = 1:numel(propnames),
C{p} = object.(propnames{p});
end
Then inside whatever function you write, you can get a comma-separated list of all properties with C{:}, which will be suitable for a function that expects each property name input as a separate argument (e.g. C = getProps(myObj,propnames); x = myFun(h,C{:}).
I made a Matlab function
function foo(argone, argtwo)
The begining of the function allow to have default choices for those variables if the function is called only with one or even zero arguments
function foo(argone, argtwo)
if(~exist('argone','var'))
argone = defaultargone;
end
if(~exist('argtwo', 'var'))
argtwo = defaultargtwo;
end
... % Rest of the code
We can call the function as
foo() % Default values are assigned to argone and argtwo
foo(myargone) % Default value given to argtwo
foo(myargone, myargtwo) % No default values are used
But how to be able to give default value to argone only?
If function is called with
foo(~, myargtwo)
no default values are used; argone get the null value (that is not the default value)
Thank you for your help
An alternate way would be to include the option for handling an empty input:
function foo(argone, argtwo)
if ~exist('argone','var')||isempty(argone)
argone = defaultargone;
end
if ~exist('argtwo','var')||isempty(argtwo)
argtwo = defaultargtwo;
end
Then any of these should work:
foo()
foo([],[])
foo(argone)
foo([], argtwo)
The language itself does not support such inputs. A common workaround uses parameter value pairs.
Usange would be
foo('myargone',1, 'myargtwo',2)
foo('myargtwo',3)
foo('myargone',4)
In your function, you have to use varargin and the input parser
How can i access the following structure path with dynamic fieldnames:
var = 'refxtree.CaseDefinition.FlowSheetObjects.MaterialStreamObjects{8}.MaterialStreamObjectParams.Pressure.Value.Text';
fields = textscan(var,'%s','Delimiter','.');
refxtree.(fields{:}) does not work because MaterialStreamObjects contains a cell array of which I want to access the 8th cell and then continue down the structure path.
In the end I want to get and set the fieldvalues.
You need to build the appropriate input to subsref, possibly using substruct. Look at the MATLAB help.
You can define an anonymous function to navigate this particular kind of structure of the form top.field1.field2.field3{item}.field4.field5.field6.field7 (as an aside: is it really necessary to have such a complicated structure?).
getField = #(top,fields,item)top.(fields{1}).(fields{2}).(fields{3}){item}.(fields{4}).(fields{5}).(fields{6}).(fields{7})
setField = #(top,fields,item,val)subsasgn(top.(fields{1}).(fields{2}).(fields{3}){item}.(fields{4}).(fields{5}).(fields{6}),struct('type','.','subs',fields{7}),val);
You use the functions by calling
fieldValue = getField(refxtree,fields,8);
setField(refxtree,fields,8,newFieldValue);
Note that fields is required to have seven elements. If you want to generalize the above, you will have to dynamically create the above functions
In this case, it is easier to just use EVAL:
str = 'refxtree.CaseDefinition.FlowSheetObjects.MaterialStreamObjects{8}.MaterialStreamObjectParams.Pressure.Value.Text';
%# get
x = eval(str)
%# set
evalc([str ' = 99']);
I have a function which accepts a variable number of input variables. The problem is, the number of input arguments I'm going to provide varies. As such, I store all the arguments in a structure:
function grandAvg(datafiles)
% Load up all averaged datafiles
avgs = struct();
for n=1:length(datafiles)
avgs(n).avg = load(datafiles{n});
end
My question is, is there a way to expand this argument for the function? I need a way to convert this:
% DOES NOT WORK
avg = ft_timelockgrandaverage(cfg, avgs);
to this:
% WOULD WORK, BUT DO NOT WANT TO TYPE IT OUT
avg = ft_timelockgrandaverage(cfg, avgs(1).avg, ..., avgs(n).avg);
EDIT TO ADD: So apparently my question wasn't clear. I know how to construct the function using varargin. My question was, if I am trying to use a build-in function which I don't want to or can't modify, how can I provide arguments in a variable manner? I.e., I don't know ahead of time how many argument's I'll be providing, so when I call the function, I'll have to call it with X number of arguments. In effect, I'm looking for a way to turn this:
someVar <1xN struct>
into this:
someVar1 <1x1 struct>
someVar2 <1x1 struct>
...
someVarN <1x1 struct>
in a programmatic manner. Thanks!
An alternative to using a structure array to store your data would be to use a cell array. For example:
nFiles = numel(datafiles); %# Number of files
avgs = cell(1,nFiles); %# Initialize an empty cell array
for iFile = 1:nFiles %# Loop over the files
avgs{iFile} = load(datafiles{iFile}); %# Load the data into each cell
end
avg = ft_timelockgrandaverage(cfg, avgs{:}); %# Pass the contents to a function
The syntax avgs{:} dumps the contents of the cell array into what's called a comma-separated list. It is equivalent to typing avgs{1}, avgs{2}, ... , avgs{end}. The syntax foo(:).bar from the answer you found also creates a comma-separated list, but I find that using cell arrays for such a purpose is generally cleaner than using a structure array.
yes you can use variable length input argument list
varargin
http://www.mathworks.com/help/techdoc/ref/varargin.html
So, after playing around, I've got it. Using the example from above:
Given an 1xN struct named foo, where each foo(n) contains the field bar, I would call the function as:
function(foo(:).bar);
This is the same as typing
function(foo(1).bar, foo(2).bar, ..., foo(N).bar);
In this way, I can dynamically expand or shrink foo and still have no problem calling the function.
You can surely do such a thing, by means of the varargin construct in MATLAB. This will be something like:
avg = ft_timelockgrandaverage(cfg, avgs.avg);
And for the function ft_timelockgrandaverage
function output = ft_timelockgrandaverage(config, varargin)
% your code here
varargin will be a cell array: {avgs(1).avg, avgs(2).avg, ..., avgs(3).avg} which you can process.