NaN when calculating average

Question

Pankaj 2012-1-22

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I read data from a .xls file using xlsread. There are some 3000 rows with price data, all in number format in excel. I further try to calculate the average of previous 10 days for every day using mean2(prices(i-10,1):prices(i,1)). I do this for last 2990 rows. surprisingly a lot of these throw NaN. I have also run a check "isnan" on each element in prices and none of them tests positive. also stumbled on something:

isnumeric(NaN)

ans =

     1
how is this working??

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Answer 1

David Young 2012-1-22

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Although a NaN is not a number, it is of class double, and so it is numeric. If a NaN was not numeric, it could not be held in a matrix with other numbers.

Your problem is that prices(i-10,1):prices(i,1) may be empty, so mean2 returns NaN. In fact, that expression doesn't look likely to be correct. I suspect you intended to use mean2(prices(i-10:i, 1)).

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Answer 2

Andrew Newell 2012-1-22

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在 MATLAB Online 中打开

You could use nanmean to ignore the NaN's while calculating means:

prices = rand(20,20);
n = size(prices,1); m = size(prices,2); window=10;
runningMean = zeros(n-window,m);
for ii=1:n-window
  runningMean(ii,:) = nanmean(runningMean(ii:ii+window-1,:));
end

Note that I am interpreting your statement of "previous 10 days" as the ten days before the current day. Your version is actually averaging 11 days.

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Atakan 2012-1-22

This is my code:

function [randnormal]=atakan(a,b,m)

randnormal=[];

count=1;

while (count<=m)

R = normrnd(a,b);

u1=unifrnd(0,1);

u2=unifrnd(0,1);

y=tan(pi*(u1-1/2));

if (u2<=((sqrt(exp(1))/2)*(1+y^2)*(exp(1)^(-y^2/2))))

randnormal=[R;y];

end

count=count+1;

end

Pankaj 2012-1-23

Thanks Andrew - good solution - it helps!

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Answer 3

Atakan 2012-1-22

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Hi; I want to ask a question to the main page. But it gives an error such that "we are sorry but something went wrong". What can I do?

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Atakan 2012-1-22

I have tried many many times. But there is still a problem. If I send the question to you, can you ask the question for me? Because this is very important for me. thanks...