Date of reference in an feature collection

Question

I am pretty new on GEE and idk how easy is this task. I want to find daily precipitation for all Brazilian municipalities in 2006. I applied a map function with reduce regions and end up with a feature collection of municipalities. But I really need the date of reference for each element (day and month). I tried to use set function but idk how to guarantee each information would have the correct date from the image that was calculated. My ending goal is a table to export to google drive.

Here's my code:

var mun = ee.FeatureCollection("users/rodrigoccuri/BRMUE250GC_SIR");

// Importing Chirps dataset:
var chirps = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY');

// Filtering year 2006:
var chirps06 = chirps.filterDate('2006-01-01', '2006-12-31');

// Creating a function to reduce regions for each image by pixel mean for mun:
var reduce = function(image) {
  return image.reduceRegions(mun, ee.Reducer.mean(), 1000)
}

// Appling reducer for each image in the collection:
var precmun06 = chirps06.map(reduce).flatten();

print(precmun06.first());

Answer 1

While mapping over your chirps data, you need to set the date on each municipality:

var reduce = function(image) {
  return image.reduceRegions(mun, ee.Reducer.mean(), 1000) A FeatureCollection of municipalities
    .map(function (feature) { // You want assign the date to each of these
      return feature // You needed month and day separately?
        .set('month', image.date().get('month'))
        .set('day', image.date().get('day'))
    })
}

https://code.earthengine.google.com/18029656e797fd35d9c0a1f37e3c0d62