I've got a set of data in an excel sheet that I've imported onto MATLAB however there are NaNs within that set of data. I've figured out some code in the main script to replace the NaN's into the wanted values:
max = x(:, 2);
min = x(:, 3);
for j = 1:length(max)
for k = 1:length(min)
if isnan (max(j))
max (j) = ((max(j-1)+max(j+1))/2);
elseif isnan (min(k))
min (k) = ((min(k-1)+min(k+1))/2);
end
end
end
However, I need to be able to turn this code into a user-defined function and call it from the main script instead of having all the calculations on the main script.
I've tried to start making the function:
function [missingmax, missingmin] = missing(max, min)
However, I could not figure the rest out.
function [max_x, min_x] = missing(x)
max_x = x(:, 2);
min_x = x(:, 3);
for jj = 1:length(max_x)
for kk = 1:length(min_x)
if isnan (max_x(jj))
max_x (jj) = ((max_x(jj-1)+max_x(jj+1))/2);
elseif isnan (min_x(kk))
min_x (kk) = ((min_x(kk-1)+min_x(kk+1))/2);
end
end
end
end
You were on the right track. Couple of things:
Your input is x, not min,max
Your outputs are min and max, not missingmax and missingmin
j denotes the imaginary unit It's not recommended for use as a variable, hence I changed it.
You called variables min and max. Don't do that. Ever. Seriously. Don't. If you manage to do min=4 and then try to calculate the minimum of an array, you'll get a bunch of errors. Basically: never use the name of a build-in function for a variable.
Since you do a linear interpolation, you don't need to define a function here. It already exists in Matlab : fillmissing
So you can replace missing values in x like that
x_filled = fillmissing(x,'linear')
Related
Suppose we are running an infinite for loop in MATLAB, and we want to store the iterative values in a vector. How can we declare the vector without knowing the size of it?
z=??
for i=1:inf
z(i,1)=i;
if(condition)%%condition is met then break out of the loop
break;
end;
end;
Please note first that this is bad practise, and you should preallocate where possible.
That being said, using the end keyword is the best option for extending arrays by a single element:
z = [];
for ii = 1:x
z(end+1, 1) = ii; % Index to the (end+1)th position, extending the array
end
You can also concatenate results from previous iterations, this tends to be slower since you have the assignment variable on both sides of the equals operator
z = [];
for ii = 1:x
z = [z; ii];
end
Sadar commented that directly indexing out of bounds (as other answers are suggesting) is depreciated by MathWorks, I'm not sure on a source for this.
If your condition computation is separate from the output computation, you could get the required size first
k = 0;
while ~condition
condition = true; % evaluate the condition here
k = k + 1;
end
z = zeros( k, 1 ); % now we can pre-allocate
for ii = 1:k
z(ii) = ii; % assign values
end
Depending on your use case you might not know the actual number of iterations and therefore vector elements, but you might know the maximum possible number of iterations. As said before, resizing a vector in each loop iteration could be a real performance bottleneck, you might consider something like this:
maxNumIterations = 12345;
myVector = zeros(maxNumIterations, 1);
for n = 1:maxNumIterations
myVector(n) = someFunctionReturningTheDesiredValue(n);
if(condition)
vecLength = n;
break;
end
end
% Resize the vector to the length that has actually been filled
myVector = myVector(1:vecLength);
By the way, I'd give you the advice to NOT getting used to use i as an index in Matlab programs as this will mask the imaginary unit i. I ran into some nasty bugs in complex calculations inside loops by doing so, so I would advise to just take n or any other letter of your choice as your go-to loop index variable name even if you are not dealing with complex values in your functions ;)
You can just declare an empty matrix with
z = []
This will create a 0x0 matrix which will resize when you write data to it.
In your case it will grow to a vector ix1.
Keep in mind that this is much slower than initializing your vector beforehand with the zeros(dim,dim) function.
So if there is any way to figure out the max value of i you should initialize it withz = zeros(i,1)
cheers,
Simon
You can initialize z to be an empty array, it'll expand automatically during looping ...something like:
z = [];
for i = 1:Inf
z(i) = i;
if (condition)
break;
end
end
However this looks nasty (and throws a warning: Warning: FOR loop index is too large. Truncating to 9223372036854775807), I would do here a while (true) or the condition itself and increment manually.
z = [];
i = 0;
while !condition
i=i+1;
z[i]=i;
end
And/or if your example is really what you need at the end, replace the re-creation of the array with something like:
while !condition
i=i+1;
end
z = 1:i;
As mentioned in various times in this thread the resizing of an array is very processing intensive, and could take a lot of time.
If processing time is not an issue:
Then something like #Wolfie mentioned would be good enough. In each iteration the array length will be increased and that is that:
z = [];
for ii = 1:x
%z = [z; ii];
z(end+1) = ii % Best way
end
If processing time is an issue:
If the processing time is a large factor, and you want it to run as smooth as possible, then you need to preallocating.If you have a rough idea of the maximum number of iterations that will run then you can use #PluginPenguin's suggestion. But there could still be a change of hitting that preset limit, which will break (or severely slow down) the program.
My suggestion:
If your loop is running infinitely until you stop it, you could do occasional resizing. Essentially extending the size as you go, but only doing it once in a while. For example every 100 loops:
z = zeros(100,1);
for i=1:inf
z(i,1)=i;
fprintf("%d,\t%d\n",i,length(z)); % See it working
if i+1 >= length(z) %The array as run out of space
%z = [z; zeros(100,1)]; % Extend this array (note the semi-colon)
z((length(z)+100),1) = 0; % Seems twice as fast as the commented method
end
if(condition)%%condition is met then break out of the loop
break;
end;
end
This means that the loop can run forever, the array will increase with it, but only every once in a while. This means that the processing time hit will be minimal.
Edit:
As #Cris kindly mentioned MATLAB already does what I proposed internally. This makes two of my comments completely wrong. So the best will be to follow what #Wolfie and #Cris said with:
z(end+1) = i
Hope this helps!
I have the following code which eventually outputs a graph and a 'groups' value. The results are dependent on a random function so can provide different results every times.
function [t seqBeliefs] = extendedHK(n, tol, adj)
%extendedHK Summary of function goes here
%Detailed explanation goes here
beliefs = rand(n,1);
seqBeliefs = beliefs; %NxT matrix
converge = 0;
step = 0
t = step
while converge ~= 1
step = step+1;
t = [t step];
A = zeros (n,n);
for i=1:1:n
for j=i:1:n
if abs(beliefs(i) - beliefs(j)) < tol && adj(i,j)==1
A(j,i)=1;
A(i,j)=1;
end
end
end
beliefs = A*beliefs./ sum(A,2);
seqBeliefs = [seqBeliefs beliefs];
if sum(abs(beliefs - seqBeliefs(:,step)))<1e-12
converge = 1;
end
end
groups = length(uniquetol(seqBeliefs(:,step), 1e-10))
plot(t,seqBeliefs)
end
In command window type
adj=random_graph(n)
I usually use n as 100 then call extendedHK function with same n then tol value (I usually choose between 0.1 and 0.4) and 'adj'
e.g. adj = random_graph(100)
extendedHK(100, 0.2, adj)
What I now need help with is running this function say 100 times, and taking an average of how many 'groups' are formed.
First, include the parameter "groups" in your function output. to do so, try this instead of the first line of your code:
function [t seqBeliefs groups] = extendedHK(n, tol, adj)
then save this function in a extendedHK.m file.
open another .m file, say console.m and write this:
results = zeros(1,100);
for i = 1:100
% set n, tol and adj inputs here <=
[~,~,out] = extendedHK(n, tol, adj);
results(1,i) = out;
end
avg = mean(results)
don't forget to define "results" out of the loop. since parameters that change size every loop, will make your code slow
(suppressing unnecessary outputs with ~ added later to this reply)
It is not clear if you need the current outputs of extendedHK:[t seqBeliefs]
Anyhow, you can add "groups" to the output and then from the console
N=100;
groups_vec = zeros(1,N);
for i=1:N
adj = random_graph(100);
[~,~,groups_vec(i)] = extendedHK(100, 0.2, adj);
end
groups_avr = mean(groups_vec);
note that if you use this code you won't be able to "see" the graphs as they will be cleared every loop iteration. you can do one of the following (1) add "figure;" before the plot command and then you will have 100 figures. (2) add "pause" to wait for key press between each graph. (3) add "hold on" to print all graphs on the same figure.
Suppose a MATLAB program is written as:
c=5;
a=4.5;
m=14;
for i=1:14
a=c*a;
end
How do I store the values of a? I wish to use the values of a later.
You need to store previous values of a in an array. You can pre-allocate the array outside of your loop and then fill it each time through your loop.
a = zeros(1, 15);
a(1) = 4.5;
for k = 1:14
a(k + 1) = c * a(k);
end
last_a = a(end);
A short form of #Suever's answer, can be written like that:
c=5;
a=4.5*c.^(0:14);
The results are:
a=
4.50000000000000 22.5000000000000 112.500000000000 562.500000000000 2812.50000000000 14062.5000000000 70312.5000000000 .......
Hi for my code I would like to know how to best save my variable column. column is 733x1. Ideally I would like to have
column1(y)=column, but I obtain the error:
Conversion to cell from logical is not possible.
in the inner loop. I find it difficult to access these stored values in overlap.
for i = 1:7
for y = 1:ydim % ydim = 436
%execute code %code produces different 'column' on each iteration
column1{y} = column; %'column' size 733x1 %altogether 436 sets of 'column'
end
overlap{i} = column1; %iterates 7 times.
end
Ideally I want overlap to store 7 variables saved that are (733x436).
Thanks.
I'm assuming column is calculated using a procedure where each column is dependent on the latter. If not, then there are very likely improvements that can be made to this:
column = zeros(733, 1); % Might not need this. Depends on you code.
all_columns = zeros(xdim, ydim); % Pre-allocate memory (always do this)
% Note that the first dimension is usually called x,
% and the second called y in MATLAB
overlap = cell(7, 1);
overlap(:) = {zeros(xdim, ydim)}; % Pre-allocate memory
for ii = 1:numel(overlap) % numel is better than length
for jj = 1:ydim % ii and jj are better than i and j
% several_lines_of_code_to_calculate_column
column = something;
all_columns(:, jj) = column;
end
overlap{ii} = all_columns;
end
You can access the variables in overlap like this: overlap{1}(1,1);. This will get the first element in the first cell. overlap{2} will get the entire matrix in the second cell.
You specified that you wanted 7 variables. Your code implies that you know that cells are better than assigning it to different variables (var1, var2 ...). Good! The solution with different variables is bad bad bad.
Instead of using a cell array, you could instead use a 3D-array. This might make processing later on faster, if you can vectorize stuff for instance.
This will be:
column = zeros(733, 1); % Might not need this. Depends on you code.
overlap = zeros(xdim, ydim, 7) % Pre-allocate memory for 3D-matrix
for ii = 1:7
for jj = 1:ydim
% several_lines_of_code_to_calculate_column
column = something;
all_column(:, jj, ii) = column;
end
end
I'm trying to create a function that reads in a field of a structure to create a vector of fields. I have a structure of the form:
subject(i).stride(j).strideLength
and there are 10 subjects, about 10 strides per subject. I can create a long vector of the strideLength of all subjects, all strides with code like this:
k = 1;
for i=1:10
for j=1:size(subject(i).stride, 2)
varVector(k) = subject(i).stride(j).strideLength;
k = k + 1;
end
end
however, there are a lot of different fields I want to do this with, and I'd like to do it with a function that I can call like this:
x(1) = groupData(strideLength);
but I can't figure out the syntax to append strideLength to subject(i).stride(j). within the above loop in a function. This is what I hoped would work and didn't:
function [varVector] = groupData(var)
%groupData returns a concatenated vector of a given variable (speed, etc.)
k = 1;
for i=1:10
for j=1:size(subject(i).stride, 2)
varVector(k) = subject(i).stride(j).var;
k = k + 1;
end
end
end
Any thoughts on how to do this right? Thanks in advance!
In your groupData function, pass in the field/variable name as a string
x(1) = groupData('strideLength');
Then in the body of the code, access this field as follows
varVector(k) = subject(i).stride(j).(var);
Try the above and see what happens!