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ee.Dictionary.map
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根据您的偏好保存内容并对其进行分类。
将算法映射到字典。该算法应接受 2 个实参,即现有字典中的键及其对应的值,并返回给定键的新值。如果算法返回 null,则会舍弃相应密钥。
用法 | 返回 |
---|
Dictionary.map(baseAlgorithm) | 字典 |
参数 | 类型 | 详细信息 |
---|
此:dictionary | 字典 | |
baseAlgorithm | 算法 | |
示例
代码编辑器 (JavaScript)
// A dictionary (e.g. results of ee.Image.reduceRegion of an S2 image).
var dict = ee.Dictionary({
B1: 182,
B2: 219,
B3: 443
});
/**
* Convert S2 surface reflectance units to native scale.
*/
function scale(key, value) {
return ee.Number(value).divide(1e4);
}
print('S2 surface reflectance in native units', dict.map(scale));
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)
# A dictionary (e.g. results of ee.Image.reduceRegion of an S2 image).
dic = ee.Dictionary({
'B1': 182,
'B2': 219,
'B3': 443
})
def scale(key, value):
"""Convert S2 surface reflectance units to native scale."""
return ee.Number(value).divide(1e4)
print('S2 surface reflectance in native units:', dic.map(scale).getInfo())
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最后更新时间 (UTC):2025-07-26。
[null,null,["最后更新时间 (UTC):2025-07-26。"],[[["\u003cp\u003e\u003ccode\u003eDictionary.map()\u003c/code\u003e applies a provided algorithm to each key-value pair in a dictionary, transforming the values based on the algorithm's logic.\u003c/p\u003e\n"],["\u003cp\u003eThe algorithm used by \u003ccode\u003eDictionary.map()\u003c/code\u003e receives a key and its corresponding value as input, and it should return the new value for that key.\u003c/p\u003e\n"],["\u003cp\u003eIf the algorithm returns null for a specific key, that key-value pair will be excluded from the resulting dictionary.\u003c/p\u003e\n"],["\u003cp\u003e\u003ccode\u003eDictionary.map()\u003c/code\u003e is particularly useful for tasks like data transformation and filtering within dictionaries, offering a concise way to modify values based on custom logic.\u003c/p\u003e\n"],["\u003cp\u003eExample use cases include converting units of measurement within a dataset or selectively removing entries based on certain criteria applied to the key-value pairs.\u003c/p\u003e\n"]]],["The core content details the `map` function for dictionaries. This function applies a user-defined algorithm to each key-value pair within a dictionary. The algorithm takes a key and its corresponding value as input and returns a new value. The `map` function iterates through the dictionary, executes the provided algorithm on each pair, and generates a new dictionary with the updated values. If the algorithm's result is `null`, the key is removed from the resulting dictionary. Examples illustrate this with scaling values in a dictionary.\n"],null,["# ee.Dictionary.map\n\nMap an algorithm over a dictionary. The algorithm is expected to take 2 arguments, a key from the existing dictionary and the value it corresponds to, and return a new value for the given key. If the algorithm returns null, the key is dropped.\n\n\u003cbr /\u003e\n\n| Usage | Returns |\n|---------------------------------|------------|\n| Dictionary.map`(baseAlgorithm)` | Dictionary |\n\n| Argument | Type | Details |\n|--------------------|------------|---------|\n| this: `dictionary` | Dictionary | |\n| `baseAlgorithm` | Algorithm | |\n\nExamples\n--------\n\n### Code Editor (JavaScript)\n\n```javascript\n// A dictionary (e.g. results of ee.Image.reduceRegion of an S2 image).\nvar dict = ee.Dictionary({\n B1: 182,\n B2: 219,\n B3: 443\n});\n\n/**\n * Convert S2 surface reflectance units to native scale.\n */\nfunction scale(key, value) {\n return ee.Number(value).divide(1e4);\n}\n\nprint('S2 surface reflectance in native units', dict.map(scale));\n```\nPython setup\n\nSee the [Python Environment](/earth-engine/guides/python_install) page for information on the Python API and using\n`geemap` for interactive development. \n\n```python\nimport ee\nimport geemap.core as geemap\n```\n\n### Colab (Python)\n\n```python\n# A dictionary (e.g. results of ee.Image.reduceRegion of an S2 image).\ndic = ee.Dictionary({\n 'B1': 182,\n 'B2': 219,\n 'B3': 443\n})\n\n\ndef scale(key, value):\n \"\"\"Convert S2 surface reflectance units to native scale.\"\"\"\n return ee.Number(value).divide(1e4)\n\nprint('S2 surface reflectance in native units:', dic.map(scale).getInfo())\n```"]]