Get an array of specific parameters from Image Collection of Google Earth Engine - google-earth-engine

Question

I've got an Image Collection like:
ImageCollection : {
features : [
0 : {
type: Image,
id: MODIS/006/MOD11A1/2019_01_01,
properties : {
LST_Day_1km : 12345,
LST_Night_1km : 11223,
system:index : "2019-01-01",
system:asset_size: 764884189,
system:footprint: LinearRing,
system:time_end: 1546387200000,
system:time_start: 1546300800000
},
1 : { ... }
2 : { ... }
...
],
...
]
From this collection, how can I get an array of objects of specific properties? Like:
[
{
LST_Day_1km : 12345,
LST_Night_1km : 11223,
system:index : "2019-01-01"
},
{
LST_Day_1km : null,
LST_Night_1km : 11223,
system:index : "2019-01-02"
}
...
];
I tried ImageCollection.aggregate_array(property) but it allows only one parameter at one time.
The problem is that the length of "LST_Day_1km" is different from the length of "system:index" because "LST_Day_1km" includes empty values, so it's hard to combine arrays after get them separately.
Thanks in advance!

Answer 1

Whenever you want to extract data from a collection in Earth Engine, it is often a straightforward and efficient strategy to first arrange for the data to be present as a single property on the features/images of that collection, using map.
var wanted = ['LST_Day_1km', 'LST_Night_1km', 'system:index'];
var augmented = imageCollection.map(function (image) {
return image.set('dict', image.toDictionary(wanted));
});
Then, as you're already familiar with, just use aggregate_array to extract that property's values:
var list = augmented.aggregate_array('dict');
print(list);
Runnable complete example:
var imageCollection = ee.ImageCollection('MODIS/006/MOD11A1')
.filterDate('2019-01-01', '2019-01-07')
.map(function (image) {
// Fake values to match the question
return image.set('LST_Day_1km', 1).set('LST_Night_1km', 2)
});
print(imageCollection);
// Add a single property whose value is a dictionary containing
// all the properties we want.
var wanted = ['LST_Day_1km', 'LST_Night_1km', 'system:index'];
var augmented = imageCollection.map(function (image) {
return image.set('dict', image.toDictionary(wanted));
});
print(augmented.first());
// Extract that property.
var list = augmented.aggregate_array('dict');
print(list);
https://code.earthengine.google.com/ffe444339d484823108e23241db04629