Google Earth Engine: Extract second largest value from annual observations? - google-earth-engine

Question

In Google Earth Engine, is it possible to extract the annual second largest and second smallest value and construct an imagecollection?
Apparently, there is no build-in reducer for this purpose.
Here is my code for getting the min, please guide me on how to get the second max and min.
Thank you!
Here is the code:
var startDate = ee.Date('2001-01-01'); // set start time for analysis
var endDate = ee.Date('2021-12-31'); // set end time for analysis
// calculate the number of year to process
var nyears = ee.Number(endDate.difference(startDate,'year'));
//init a time band
var createTimeBand= function(image) {
return image.addBands(image.metadata('system:time_start')
.divide(1e18))
// .divide(1000*60*60*24*365))
}
var sst = ee.ImageCollection('MODIS/006/MOD11A1').select('LST_Day_1km')
.filterDate(startDate, endDate)
.map(createTimeBand)
var byyearMin = ee.ImageCollection(
// map over each month
ee.List.sequence(0,nyears).map(function (n) {
// calculate the offset from startDate
var ini = startDate.advance(n,'year');
// advance just one month
var end = ini.advance(1,'year');
// filter and reduce
return sst.filterDate(ini,end)
.select(0).min()
// .sort('LST_Day_1km').reverse().first()
.multiply(0.02)
.subtract(273.15)
.set('system:time_start', ini.millis());//convert time to number
}));

Answer 1

var startDate = ee.Date('2001-01-01'); // set start time for analysis
var endDate = ee.Date('2021-12-31'); // set end time for analysis
// calculate the number of year to process
var nyears = ee.Number(endDate.difference(startDate,'year'));
//init a time band
var createTimeBand= function(image) {
return image.addBands(image.metadata('system:time_start')
.divide(1e18))
// .divide(1000*60*60*24*365))
}
var sst = ee.ImageCollection('MODIS/006/MOD11A1').select('LST_Day_1km')
.filterDate(startDate, endDate)
//.map(createTimeBand)
var byyearMin = ee.ImageCollection(
// map over each month
ee.List.sequence(0,nyears).map(function (n) {
// calculate the offset from startDate
var ini = startDate.advance(n,'year');
// advance just one month
var end = ini.advance(1,'year');
var sortedDays = sst.filterDate(ini,end)
.sort('LST_Day_1km')
.toList(sst.size())
var secondLargest = ee.List(sortedDays.get(1))
var secondSmallest = ee.List(sortedDays.get(-1))
var collection = ee.Image(secondLargest)
.addBands(secondSmallest).rename(['secondLargest', 'secondSmallest'])
.multiply(0.02)
.subtract(273.15)
return collection
.set('system:time_start', ini.millis()) //convert time to number
.set('Date', ee.Date(ini))
}));
print(byyearMin)