Calculating min and max values in a feature collection column, ignoring non-numeric strings in Google Earth Engine

Question

How to find the min and max values of a column in a feature collection, disregarding values that cannot be converted to numbers (e.g., "NA" and "No data")? I still need to find a server-side solution for this, and I'm avoiding using getInfo() because the array returned may be too large.

Consider this feature collection as an example:

var fc = ee.FeatureCollection([
  ee.Feature(null, {a: '10', b: '9.80', c: '100'}),
  ee.Feature(null, {a: 'NA', b: '1.35', c: '200'}),
  ee.Feature(null, {a: 'NA', b: '4.85', c: 'NA'}),
  ee.Feature(null, {a: '30', b: 'NA', c: '300'}),
  ee.Feature(null, {a: '80', b: '1.25', c: '400'}),
]);

Answer 1

If your data is well-formed, you can simply filter out everything that's "NA" (or any other specific "bad" values like null) and then turn everything that's left into a number with Number.parse.

print(fc.filter(ee.Filter.neq("a", "NA"))
      .map(function(f) {
          return f.set("a", ee.Number.parse(f.get("a")))
      })
      .reduceColumns(ee.Reducer.minMax(), ["a"]))

You'll have to do this separately for each column (which you can do by mapping over propertyNames)

Answer 2

An alternative to the solution proposed by Noel:

var fc = ee.FeatureCollection([
  ee.Feature(null, {a: '10', b: '9.80', c: '100'}),
  ee.Feature(null, {a: 'NA', b: '1.35', c: '200'}),
  ee.Feature(null, {a: '20', b: '4.85', c: 'NA'}),
  ee.Feature(null, {a: '30', b: 'NA', c: '300'}),
  ee.Feature(null, {a: '80', b: '1.25', c: '400'}),
]);

var property = 'a';
var array = fc.aggregate_array(property);

array = array.map(function(s) {
  return ee.Algorithms.If({
    condition: ee.String(s).match('^\\D'),
    trueCase: null,
    falseCase: ee.Number.parse(s)
  });
}, true);

var minMax = array.reduce(ee.Reducer.minMax());
print('minMax', minMax);

// Output
minMax
{
  "max": 80,
  "min": 10
}