replace nan with a value

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Daphne Mariaravi 2017-6-21

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评论： Star Strider 2017-6-21

I have a column in which some values are missing and shown as NaN. I need to replace all these NaN with the median of the column. Here is what I tried: I am extracting column 4 in which there are missing values, find the median value, Use isnan to replace the logical 1 with the median.

Column 4 values: 1 2 3 4 5 6 NaN 12 10 NaN 4 5 NaN

     C=num(:,4);
     median=nanmedian(C);
     R(isnan(C))=median;

But with this I am getting results as : 0 0 0 0 0 0 12 0 0 12 0 0 12

But the expected result is: 1 2 3 4 5 6 12 12 10 12 4 5 12

Any suggestions ?

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Answer 1

Star Strider 2017-6-21

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Please do not use ‘median’ as a variable name.

I don’t know where the ‘12’ value comes from, since the median of the vector you posted is 4.5.

Other than that, ‘R’ does not magickally become ‘C’. You have to create it first.

This works for me:

C = [1 2 3 4 5 6 NaN 12 10 NaN 4 5 NaN]';
median_4 = nanmedian(C);
R = C;
R(isnan(C)) = median_4;

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Daphne Mariaravi 2017-6-21

The median value 12 wasn't actually calculated. I just filled in some random values just to give a picture of what my problem was. Sorry about that. The code works! Thanks

Star Strider 2017-6-21

My pleasure!

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Answer 2

Steven Lord 2017-6-21

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If you're using release R2016b or later use fillmissing.

z = [1 2 3 4 5 6 NaN 12 10 NaN 4 5 NaN].';
y = fillmissing(z, 'constant', median(z, 'omitnan'));
showBothColumnsSideBySide = [z, y]

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Jan 2017-6-21

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@Daphne: This happens, because "median" was defined as a variable on your computer. Do not shadow builtin functions by variables. Solution: Restart Matlab or:

clear median

Daphne Mariaravi 2017-6-21