ee.FeatureCollection.reduceColumns

使用给定的选择器确定输入，然后将化简器应用于集合的每个元素。

返回一个结果字典，其中包含以输出名称为键的结果。

用法	返回
FeatureCollection.reduceColumns(reducer, selectors, weightSelectors)	字典

参数	类型	详细信息
此：collection	FeatureCollection	要汇总的集合。
reducer	缩减器	要应用的缩减器。
selectors	列表	针对每个 reducer 输入的选择器。
weightSelectors	列表，默认值：null	用于选择每个加权 reducer 输入的 selector。

示例

代码编辑器 (JavaScript)

// FeatureCollection of power plants in Belgium.
var fc = ee.FeatureCollection('WRI/GPPD/power_plants')
            .filter('country_lg == "Belgium"');

// Calculate mean of a single FeatureCollection property.
var propMean = fc.reduceColumns({
  reducer: ee.Reducer.mean(),
  selectors: ['gwh_estimt']
});
print('Mean of a single property', propMean);

// Calculate mean of multiple FeatureCollection properties.
var propsMean = fc.reduceColumns({
  reducer: ee.Reducer.mean().repeat(2),
  selectors: ['gwh_estimt', 'capacitymw']
});
print('Mean of multiple properties', propsMean);

// Calculate weighted mean of a single FeatureCollection property. Add a fuel
// source weight property to the FeatureCollection.
var fuelWeights = ee.Dictionary({
  Wind: 0.9,
  Gas: 0.2,
  Oil: 0.2,
  Coal: 0.1,
  Hydro: 0.7,
  Biomass: 0.5,
  Nuclear: 0.3
});
fc = fc.map(function(feature) {
  return feature.set('weight', fuelWeights.getNumber(feature.get('fuel1')));
});

var weightedMean = fc.reduceColumns({
  reducer: ee.Reducer.mean(),
  selectors: ['gwh_estimt'],
  weightSelectors: ['weight']
});
print('Weighted mean of a single property', weightedMean);

Python 设置

如需了解 Python API 和如何使用 geemap 进行交互式开发，请参阅 Python 环境页面。

import ee
import geemap.core as geemap

Colab (Python)

# FeatureCollection of power plants in Belgium.
fc = ee.FeatureCollection('WRI/GPPD/power_plants').filter(
    'country_lg == "Belgium"')

# Calculate mean of a single FeatureCollection property.
prop_mean = fc.reduceColumns(**{
    'reducer': ee.Reducer.mean(),
    'selectors': ['gwh_estimt']
    })
display('Mean of a single property:', prop_mean)

# Calculate mean of multiple FeatureCollection properties.
props_mean = fc.reduceColumns(**{
    'reducer': ee.Reducer.mean().repeat(2),
    'selectors': ['gwh_estimt', 'capacitymw']
    })
display('Mean of multiple properties:', props_mean)


# Calculate weighted mean of a single FeatureCollection property. Add a fuel
# source weight property to the FeatureCollection.
def get_fuel(feature):
  return feature.set('weight', fuel_weights.getNumber(feature.get('fuel1')))

fuel_weights = ee.Dictionary({
    'Wind': 0.9,
    'Gas': 0.2,
    'Oil': 0.2,
    'Coal': 0.1,
    'Hydro': 0.7,
    'Biomass': 0.5,
    'Nuclear': 0.3
    })

fc = fc.map(get_fuel)

weighted_mean = fc.reduceColumns(**{
    'reducer': ee.Reducer.mean(),
    'selectors': ['gwh_estimt'],
    'weightSelectors': ['weight']
    })
display('Weighted mean of a single property:', weighted_mean)