NDVI time-series for multiple years in Google Earth Engine

Question

I am trying to create a script and chart in GEE for NDVI time series for several years using LANDSAT/LC08/C01/T1_32DAY_NDVI collection. I developed a short script using GEE library, but the chart shows only for one year instead (and I don't even know which year) of showing for all of them (I need to compare NDVI for different years for my study area): https://code.earthengine.google.com/756d3ff7b718d91582535fd7669d0842

var countries = ee.FeatureCollection("FAO/GAUL/2015/level2");

var uzbekistan = countries.filter(ee.Filter.eq('ADM0_NAME','Uzbekistan'));

var bostanliq =uzbekistan.filter(ee.Filter.eq('ADM2_NAME','Bostanlik district'));
Map.addLayer(bostanliq, {}, "Bostanliq");

///
var dataset = ee.ImageCollection('LANDSAT/LC08/C01/T1_32DAY_NDVI')
                  .filter(ee.Filter.or(
                         ee.Filter.date('2014-01-01', '2015-01-01'),
                         ee.Filter.date('2015-01-01', '2016-01-01'),
                         ee.Filter.date('2016-01-01', '2017-01-01'),
                       ee.Filter.date('2017-01-01', '2018-01-01')))
                  .filterBounds(bostanliq);

var dataset = dataset.select('NDVI');
var colorizedVis = {
  min: 0,
  max: 1,
  palette: [
    'ffffff', 'ce7e45', 'df923d', 'f1b555', 'fcd163', '99b718', '74a901',
    '66a000', '529400', '3e8601', '207401', '056201', '004c00', '023b01',
    '012e01', '011d01', '011301'
  ],
};

///
var chart =
    ui.Chart.image
        .doySeries({
          imageCollection: dataset,
          region: bostanliq,
          regionReducer: ee.Reducer.mean(),
          scale: 30,
          yearReducer: ee.Reducer.mean(),
          startDay: 1,
          endDay: 365
        })
        .setOptions({
          title: 'Average Vegetation Index Value by Day of Year for Bostanliq',
          hAxis: {
            title: 'Day of year',
            titleTextStyle: {italic: false, bold: true}
          },
          vAxis: {
            title: 'Vegetation index',
            titleTextStyle: {italic: false, bold: true}
          },
          lineWidth: 3,
          colors: ['1d6b99', '39a8a7', '9c4f97'],
        });
print(chart);

Answer 1

You can use series method instead. Complete script looks as follows:

var countries = ee.FeatureCollection("FAO/GAUL/2015/level2");

var uzbekistan = countries.filter(ee.Filter.eq('ADM0_NAME','Uzbekistan'));

var bostanliq =uzbekistan.filter(ee.Filter.eq('ADM2_NAME','Bostanlik district'));
Map.addLayer(bostanliq, {}, "Bostanliq");

///
var dataset = ee.ImageCollection('LANDSAT/LC08/C01/T1_32DAY_NDVI')
                  .filter(ee.Filter.or(
                         ee.Filter.date('2014-01-01', '2015-01-01'),
                         ee.Filter.date('2015-01-01', '2016-01-01'),
                         ee.Filter.date('2016-01-01', '2017-01-01'),
                       ee.Filter.date('2017-01-01', '2018-01-01')))
                  .filterBounds(bostanliq);

var dataset = dataset.select('NDVI');
var colorizedVis = {
  min: 0,
  max: 1,
  palette: [
    'ffffff', 'ce7e45', 'df923d', 'f1b555', 'fcd163', '99b718', '74a901',
    '66a000', '529400', '3e8601', '207401', '056201', '004c00', '023b01',
    '012e01', '011d01', '011301'
  ],
};

///
var chart =
    ui.Chart.image
        .series({
          imageCollection: dataset,
          region: bostanliq,
          reducer: ee.Reducer.mean(),
          scale: 30,
          //yearReducer: ee.Reducer.mean(),
          //startDay: 1,
          //endDay: 365
        })
        .setOptions({
          title: 'Average Vegetation Index Value by Year for Bostanliq',
          hAxis: {
            title: 'Dates',
            titleTextStyle: {italic: false, bold: true}
          },
          vAxis: {
            title: 'Vegetation index',
            titleTextStyle: {italic: false, bold: true}
          },
          lineWidth: 1,
          colors: ['1d6b99', '39a8a7', '9c4f97'],
        });
print(chart);

After running it at GEE code editor, I got the result split by years as follows:

Editing Note:

For graphing each year separately, it can be created a new series for each year renaming NDVI band with its respective year as follows.

var countries = ee.FeatureCollection("FAO/GAUL/2015/level2");

var uzbekistan = countries.filter(ee.Filter.eq('ADM0_NAME','Uzbekistan'));

var bostanliq =uzbekistan.filter(ee.Filter.eq('ADM2_NAME','Bostanlik district'));
Map.addLayer(bostanliq, {}, "Bostanliq");

var dataset = ee.ImageCollection('LANDSAT/LC08/C01/T1_32DAY_NDVI');

var dates_list = ee.List([['2014-01-01', '2015-01-01'],
                          ['2015-01-01', '2016-01-01'],
                          ['2016-01-01', '2017-01-01'],
                          ['2017-01-01', '2018-01-01']
                          ]);

var new_dataset = dates_list.map(function (ele) {
  
  var new_dataset = dataset.filter(ee.Filter.date(ee.String(ee.List(ele).get(0)), 
                                                  ee.String(ee.List(ele).get(1))));
  
  var new_band = ee.String('NDVI_').cat(ee.String(ee.List(ele).get(0)).slice(0,4));
  
  new_dataset = new_dataset.map(function (e) {
  
    return ee.Image(e).rename(new_band);
  
  });
  
  return new_dataset.toList(new_dataset.size());
  
});

new_dataset = ee.ImageCollection(new_dataset.flatten());

//print(new_dataset);

var chart =
    ui.Chart.image
        .series({
          imageCollection: new_dataset,
          region: bostanliq,
          reducer: ee.Reducer.mean(),
          scale: 30,
        })
        .setOptions({
          title: 'Average Vegetation Index Value by Year for Bostanliq',
          hAxis: {
            title: 'Dates',
            titleTextStyle: {italic: false, bold: true}
          },
          vAxis: {
            title: 'Vegetation index',
            titleTextStyle: {italic: false, bold: true}
          },
          lineWidth: 3,
          colors: ['red', 'green', 'blue', 'orange'],
        });

print(chart);

Complete code here and the result at following picture.