MATLAB: Removing highest and lowest 5% of data as outliers using prctile

MATLABoutlierspercentagepercentileprctile

I have some numerical data imported from an Excel sheet in a column. I want to remove the highest 5% and the lowest 5% of these numbers as outliers using the prctile function. How can I do this?

Thanks in advance!

Best Answer

% Data values are in X; X2 holds remaining values after outliers removed
Y = prctile(X,[5,95]);
X2 = X(X>Y(1) & X<Y(2));  % maybe you want >= and <=, depending on your definition of outlier

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MATLAB: How to give ranking from highest to lowest

This should give you the rank you are asking for, Mekala:

   [~,p] = sort(Data,'descend');
   r = 1:length(Data);
   r(p) = r;

'r' will be the ranking.

MATLAB: Question about rmoutliers () function

Outliers using the quartile method are usually identified as values greater than Q3+1.5*IQR or less than Q1-1.5*IQR where IQR is the interquartile range, Q1 and Q3 are the 25th and 75th percentiles.

What's the logic behind adding 3 to the upper range and adding 1 plus flipping the sign of the lower range? I don't think this is what you want to do.

Nevertheless, you can compute the outliers directly without using rmoutliers by using these simple steps.

1) Compute the interquartile range.

iqrng = iqr(data);

2) Compute Q1 and Q3

Q1Q3 = prctile(data, [25,75]);

3) Create logical array identifying outliers

isOut = data > Q1Q3(2) + 3+1.5*iqrng | data < Q1Q3(1) - 1-1.5*iqrng
%                     * ^^^                           * ^^^^^ ???????

*I highly doubt this is how you want to define the outliers. I can't imagine how it would be useful.

To remove the outliers,

data(isOut) = []; 
% or 
data(isOut) = NaN;

Best Answer

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