use the ave function in r in javascript

The ave function in R is used to group a vector by a factor variable and then calculate the mean within each group. Unfortunately, there is no built-in ave function in Javascript. However, you can write your own function to perform a similar task.

Here's an example of how to write a function in Javascript that operates similarly to ave in R:


index.tsx
function ave(arr, groupBy) {
  const groups = {};
  const result = [];

  for (let i = 0; i < arr.length; i++) {
    const value = arr[i];
    const group = groupBy[i];

    if (group in groups) {
      groups[group].push(value);
    } else {
      groups[group] = [value];
    }
  }

  for (let group in groups) {
    const groupValues = groups[group];
    const mean = groupValues.reduce((sum, x) => sum + x, 0) / groupValues.length;
    for (let i = 0; i < groupValues.length; i++) {
      result.push(mean);
    }
  }

  return result;
}
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You can use the function by passing in an array to group and a parallel array of factor levels to group by. For example:


index.tsx
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const groupBy = ['A', 'B', 'A', 'B', 'C', 'D', 'C', 'D', 'A', 'B'];

console.log(ave(arr, groupBy)); // [4, 3, 4, 3, 5, 6, 5, 6, 4, 3]
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This example groups the array arr by the corresponding group values in groupBy, and then calculates the mean within each group. The result is an array of means that corresponds to the original order of arr.

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