I would be happy to hear somebody explain me the meaning of 1: before the function below please.
yActual = data2_test.Response;
x = 1:numel(yActual)';
A single colon operator in the context of your snippet is a short-hand way of creating a vector:
start_number:end_number
equivalent to
[start_number, start_number+1, start_number+2, ... end_number-1,end_number]
In your specific case, the variable x is a vector from 1,2,3... up to the number of elements in data2_test.Response.
Related
Consider the arbitrary function:
function myFunc_ = myFunc(firstInput, secondInput)
myFunc_ = firstInput * secondInput;
end
Now imagine I want to map the above function to an array for the first input firstInput, while the second input secondInput is constant. For example, something like:
firstVariable = linspace(0., 1.);
plot(firstVariable, map(myFunc, [firstVariable , 0.1]))
where 0.1 is an arbitrary scalar value for the secondInput and firstVariable array is an arbitrary array for the firstInput.
I have looked into the arrayfun() function. However, I don't know how to include the constant variable. Plus it seems like the syntax between MATLAB and Octave are different, or maybe I'm mistaken. It is important for me to have a cross-compatible code that I can share with colleagues.
Assuming in the original function you were multiplying two scalars and you want to vectorise, then
function myFunc_ = myFunc(firstInput, secondInput)
myFunc_ = firstInput .* secondInput;
end
should work just fine.
Then plot it directly:
plot( firstVariable, myFunc(firstVariable , 0.1) )
I'm afraid the arbitrary examples given in the original question were too simplified and as a result, they do not represent the actual issue I'm facing with my code. But I did manage to find the right syntax that works inside Octave:
plot(firstVariable, arrayfun(#(tempVariable) myFunc(tempVariable, 0.1), firstVariable))
basically the
#(tempVariable) myFunc(tempVariable, 0.1)
creates what is so-called an anonymous function and the
arrayfun(<function>, <array>)
maps the function over the given array.
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.
I am wondering if its possible to have conditional statements in a function argument.
for ex,
testarray = [1,5,8,5,7,23,61,16]
psum = sum(testarray>2 & testarray<10)
will it possible to implement something like this in matlab.
I would really appreciate an example.
Yes, please see the example below using your data.
testarray = [1,5,8,5,7,23,61,16]; % your array
Find sum of all numbers greater than 2 and less than 10 in testarray
psum = sum(testarray(testarray>2 & testarray<10));
The idea is that you find the indices of the numbers that meet the condition (i.e., testarray>2 & testarray<10 in this case), extract the numbers by indexing into testarray, and then sum them.
I have a char array A which basically contains a list of files names (each row one file)
(char, 526x26)
val =
0815_5275_UBA_A_1971.txt
0815_5275_UBA_A_1972.txt
0823_6275_UBA_A_1971.txt
0823_6275_UBA_A_1972.txt
0823_6275_UBA_A_1973.txt
...
I also have a variable
B = '0815_5275'
I'd like to select all rows (filenames) that start with B and save them in a new array C.
This should be simple, but somehow I can't make it work.
I've got this:
C = A(A(:,1:9) == B);
but I get the error message:
Error using ==
Matrix dimensions must agree.
I do not know in advance how many rows will match, so I can not pre-define an empty array.
thanks, any help is appreciated!
Try ismember(A(:, 1:numel(B)), B, 'rows') rather to get a logical vector that indexes only the rows you want
and now
A(C,:) to extract the rows
The reason you're getting a dimension mismatch error is because your A(:,1:9) has many rows but B only has one and Matlab does not automatically broadcast like Octave or Python. You could do it using either repmat or bsxfun but in this case ismember is the correct function to choose.
Just a simple nesting question:
I've got a <100x100 double> matrix mat_B, with I cumsum. From the resulting matrix mat_A, I just need the last row vec_C, which I need to cumsum again. My code looks like this:
mat_A = cumsum(mat_B);
vec_C = cumsum(mat_A(end,:));
My question is, if it's possible to put all of this inside one line of code. I know that cumsum(mat_B) returns a matrix, but if I put (end, :) behind the expression, it won't work.
I know it sounds quite silly, but I'd like to know how nesting works in those kind of situations.
You could skip the first cumsum and just use sum, since the last line of cumsum is equivalent to the result of sum:
>> mat_B=rand(5);
>> cumsum(mat_B)
ans =
0.2517 0.4522 0.8838 0.3751 0.2527
0.6847 0.7778 1.3412 0.7487 0.8376
1.5270 1.1579 2.1404 1.2327 1.3613
1.7115 2.0444 2.2745 2.2021 1.5247
2.2197 2.8056 2.3398 2.5442 2.0111
>> sum(mat_B)
ans =
2.2197 2.8056 2.3398 2.5442 2.0111
Therefore
vec_C = cumsum(sum(mat_B));
should do what you want.