Accessing item in list of lists using Google Earth Engine

Question

How do I access an item in a list of lists in GEE?
I know that using the method get() returns the element at the specified position in list. But the result of list.get(0) is [1, 2, 3], and I want the first element of each list in the list.
var list = ee.List([
  [1, 2, 3],
  [2, 4, 5],
  [3, 4, 5]
]);

Kevin Reid · Accepted Answer

Usually when you want to do something with each item in a list, you use map. In this case since you want the first element, you put .get(0) inside the map function.
var list = ee.List([[1, 2, 3], [10, 20, 30], [100, 200, 300]]);

print(list.map(function (innerList) {
  return ee.List(innerList).get(0);
}));

// Prints: [1,10,100]

This example contains ee.List(innerList).get(0) instead of innerList.get(0) because the map doesn't know that every element of list is a list — this cast is necessary in most cases when you map over a list to specify the expected type so you can call .get or other specific method on it.

Accessing item in list of lists using Google Earth Engine

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