Feature causing error in Climate linear regression analysis

Question

In my code, for an unknown reason one of the features (in a FC with a few thousand conflict locations and their dates) is causing a problem leading to this error: FeatureCollection (Error) Error in map(ID=00000000000000001ae5): Number.subtract: Parameter 'left' is required. When I print it, it does't seem to be different.

I know that it cannot be a problem with the FC because the same FC works together with an other Image Collection in a script doing the same thing.

Also when I limit the FC to exclude number 137 (ID=00000000000000001ae5) then the script works. var conflicts = ee.FeatureCollection('users/welp1992/Conflicts25_Date').limit(136)

This is the FC: https://code.earthengine.google.com/?asset=users/welp1992/Conflicts25_Date

And this the Code: https://code.earthengine.google.com/?accept_repo=users/welp1992/Master

Answer 1

To debug properly, do the following:

run the code with only that feature Do this without a map(), so you can print intermediate steps

var feat = ee.Feature(conf.filter(ee.Filter.eq('system:index', '00000000000000001ae5')).first())
// You will see that there are null values
var slope = addSlopes(feat);

Adding to map reveals why: image collection has masked values at the point

Map.centerObject(feat, 10)
Map.addLayer(feat)
Map.addLayer(timeSeries)

A workaround is to filter the feature collection on null values (beforeSlope and afterSlope) and then calculate the slope change for only non-null features. Thus, you will calculate the 'slopeChange' property after filtering for null values.

var conflictsWithSlopes = conflicts.map(addSlopes)
var filtNulls = conflictsWithSlopes.filter(ee.Filter.notNull(['beforeSlope', 'afterSlope']));
var withSlopeChange = filtNulls.map(function(feat){
  return ee.Feature(feat).set('slopeChange', 
          feat.getNumber('afterSlope').subtract(feat.getNumber('beforeSlope')))
});
print('withSlopeChange', withSlopeChange)

See here a reproducible example of how to debug within a function, outside server-side mapping over a collection.

PS: you link did not work as you did not copy the full link