Announcement: All noncommercial projects registered to use Earth Engine before April 15, 2025 must verify noncommercial eligibility to maintain Earth Engine access.
Stay organized with collections
Save and categorize content based on your preferences.
Iterate an algorithm over a list. The algorithm is expected to take two objects, the current list item, and the result from the previous iteration or the value of first for the first iteration.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2024-06-05 UTC."],[[["\u003cp\u003e\u003ccode\u003eList.iterate\u003c/code\u003e repeatedly applies a given algorithm to each element of a list, using the previous iteration's result.\u003c/p\u003e\n"],["\u003cp\u003eThe provided algorithm takes two arguments: the current list element and the previous result (or an initial value for the first iteration).\u003c/p\u003e\n"],["\u003cp\u003e\u003ccode\u003eList.iterate\u003c/code\u003e returns the final result after processing all elements.\u003c/p\u003e\n"],["\u003cp\u003eThis function is useful for accumulating values, applying recursive operations, or building complex sequences based on list elements.\u003c/p\u003e\n"]]],[],null,["# ee.List.iterate\n\nIterate an algorithm over a list. The algorithm is expected to take two objects, the current list item, and the result from the previous iteration or the value of first for the first iteration.\n\n\u003cbr /\u003e\n\n| Usage | Returns |\n|---------------------------------|---------|\n| List.iterate`(function, first)` | Object |\n\n| Argument | Type | Details |\n|--------------|-----------|---------|\n| this: `list` | List | |\n| `function` | Algorithm | |\n| `first` | Object | |\n\nExamples\n--------\n\n### Code Editor (JavaScript)\n\n```javascript\n// This example uses the ee.List.iterate function to generate a series of\n// sequentially halved values.\n\n// Declare a list that will hold the series of sequentially halved values,\n// initialize it with the starting quantity.\nvar quantityList = [1000];\n\n// Define the number of iterations as a list sequence.\nvar nSteps = ee.List.sequence(1, 10);\n\n// Declare a function that takes the current element of the iteration list and\n// the returned result of the previous iteration as inputs. In this case, the\n// the function is returning an accumulating list of quantities that are reduced\n// by half at each iteration.\nvar halfOfPrevious = function(currentElement, previousResult) {\n var previousQuantity = ee.Number(ee.List(previousResult).get(-1));\n var currentQuantity = previousQuantity.divide(2);\n return ee.List(previousResult).add(currentQuantity);\n};\n\n// Apply the function to the nSteps list, each element is an iteration.\nquantityList = ee.List(nSteps.iterate(halfOfPrevious, quantityList));\n\n// Display the results. Note that step 0 is included for the initial value.\nprint('Steps in the iteration of halved quantities', nSteps);\nprint('Series of sequentially halved quantities', quantityList);\nprint(ui.Chart.array.values({\n array: quantityList,\n axis: 0,\n xLabels: ee.List([0]).cat(nSteps)\n}));\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\nimport matplotlib.pyplot as plt\n\n# This example uses the ee.List.iterate function to generate a series of\n# sequentially halved values.\n\n# Declare a list that will hold the series of sequentially halved values,\n# initialize it with the starting quantity.\nquantity_list = [1000]\n\n# Define the number of iterations as a list sequence.\nn_steps = ee.List.sequence(1, 10)\n\n\n# Declare a function that takes the current element of the iteration list and\n# the returned result of the previous iteration as inputs. In this case, the\n# the function is returning an accumulating list of quantities that are reduced\n# by half at each iteration.\ndef half_of_previous(current_element, previous_result):\n previous_quantity = ee.Number(ee.List(previous_result).get(-1))\n current_quantity = previous_quantity.divide(2)\n return ee.List(previous_result).add(current_quantity)\n\n\n# Apply the function to the n_steps list, each element is an iteration.\nquantity_list = ee.List(n_steps.iterate(half_of_previous, quantity_list))\n\n# Display the results.\ndisplay('Steps in the iteration of halved quantities', n_steps)\ndisplay('Series of sequentially halved quantities', quantity_list)\nquantity_list_client = quantity_list.getInfo()\nplt.scatter(range(len(quantity_list_client)), quantity_list_client)\nplt.show()\n```"]]