Writing code for monthly NDVI medians in Google Earth Engine?

Question

My goal is to get monthly NDVI medians in Google Earth Engine. This helpful post got me started: reduce image collection to get annual monthly sum precipitation

However, I am using Landsat (not MODIS). This script does run but the map layer has "no bands to visualize".

1. How can I visualize the bands? (Maybe the issue is that this dataset only has 1 band?).
2. How can I add all 12 map layers, one per month? (perhaps with stacking?)

var ndvi = ee.ImageCollection('LANDSAT/LT5_L1T_32DAY_NDVI');

var months = ee.List.sequence(1, 12);

// Group by month, and then reduce within groups by mean();
// the result is an ImageCollection with one image for each
// month.
var byMonth = ee.ImageCollection.fromImages(
  months.map(function (m) {
    return ndvi.filter(ee.Filter.calendarRange(m, m, 'month'))
                .select().median()
                .set('month', m);
}));
print(byMonth);

Map.addLayer(ee.Image(byMonth.first()));

Answer 1

For the record, here is a good way to do this:

var imageCollection = ee.ImageCollection("LANDSAT/LT05/C01/T1");
var months = ee.List.sequence(1, 12);

var composites = ee.ImageCollection.fromImages(months.map(function(m) {
  var filtered = imageCollection.filter(ee.Filter.calendarRange({
    start: m,
    field: 'month'
  }));
  var composite = ee.Algorithms.Landsat.simpleComposite(filtered);
  return composite.normalizedDifference(['B4', 'B3']).rename('NDVI')
      .set('month', m);
}));
print(composites);

var check = ee.Image(composites.first());
Map.addLayer(check, {min: 0, max: 1}, 'check');

For the search robots, this is a "temporally grouped reduction."

Answer 2

I found another way to get multi-annual monthly (and seasonal) NDVI medians. It's based on this useful post: Selection of only monthly data on Google earth engine

The code is not elegant but it gets the job done (I define variables for each month and season instead of looping through them). Hopefully it's useful! https://code.earthengine.google.com/cc2e0f6c4f67885405236024abea0d86