Numpy - Replace a number with NaN

python arrays numpy nan gdal
Jzl5325 picture Jzl5325 · Jul 15, 2011 · Viewed 122.5k times · Source

I am looking to replace a number with NaN in numpy and am looking for a function like numpy.nan_to_num, except in reverse.

The number is likely to change as different arrays are processed because each can have a uniquely define NoDataValue. I have see people using dictionaries, but the arrays are large and filled with both positive and negative floats. I suspect that it is not efficient to try to load all of these into anything to create keys.

I tried using the following and numpy requiring that I use any() or all(). I realize that I need to iterate element wise, but hope that a built-in function can achieve this.

def replaceNoData(scanBlock, NDV):
    for n, i in enumerate(array):
        if i == NDV:
            scanBlock[n] = numpy.nan

NDV is GDAL's no data value and array is a numpy array.

Is a masked array the way to go perhaps?

Answer

Paul picture Paul · Jul 15, 2011 
A[A==NDV]=numpy.nan

A==NDV will produce a boolean array that can be used as an index for A

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