Data normalization using robust scaling

Hello all, I am trying to implement "Robust Scaling" but I am confused. Should I use "all" argument for "median" and "iqr" functions?

Thanks for the help.

DataSet = readtable('Datasets/Test.csv');
DataSet = table2array(DataSet);  % Row:7195 x Colums:22

RScaling = (DataSet - median(DataSet))./iqr(DataSet)

Answer 1

[Voss]

If you want to normalize all columns the same way (i.e., using the median and inter-quartile range of the entire data set), then use "all".

If you want to normalize each column separately (i.e., using each column's own median and inter-quartile range), then do not use "all". And in this case, it's best to use the dim argument set to 1, to explicitly say you want the median and iqr by column, in order to properly handle the situation that your data set has only one row.

[MB]

Thank you for your answer. So, I can normalize each column separately or all columns together. I want to explore the effects of various normalization techniques on clustering. I've experimented with the methods defined in the "normalize" function without specifying the "dim" argument. If I understand correctly, this normalizes each column separately. "If A is a matrix, then normalize operates on each column of A separately."

RScaling = (DataSet - median(DataSet, 1))./iqr(DataSet, 1)

[Voss]

You're welcome!

"If I understand correctly, this normalizes each column separately. "If A is a matrix, then normalize operates on each column of A separately.""

That's right. For a matrix that's not a vector, the default dim is 1, so you don't have to specify it (but it doesn't hurt to specify it). However, if you ever had the situation where your data set had one row, then you would need to specify dim as 1 if you want to normalize by column. Therefore, it's a good idea to always include the dim as 1. That's all I was suggesting.

Example: Matrix:

data = [1 2 3; 4 5 6] % non-vector matrix

data = 2x3

1 2 3 4 5 6

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normalize(data) % normalize each column

ans = 2x3

-0.7071 -0.7071 -0.7071 0.7071 0.7071 0.7071

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normalize(data,1) % same

ans = 2x3

-0.7071 -0.7071 -0.7071 0.7071 0.7071 0.7071

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normalize(data,2) % normalize each row

ans = 2x3

-1 0 1 -1 0 1

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Row vector (matrix with one row):

data = [1 2 3] % row vector

data = 1x3

1 2 3

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normalize(data) % without the dim specified, this normalizes all together this time

ans = 1x3

-1 0 1

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normalize(data,1) % normalize each column

ans = 1x3

NaN NaN NaN

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normalize(data,2) % normalize each row (same as all together in this case)

ans = 1x3

-1 0 1

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[MB]

Many thanks.

[Voss]

You're welcome!