List.Transform

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The M Code Behind the Power Query M function List.Transform

Understanding the List.Transform Function

The List.Transform function takes two arguments: a list and a function. The function applies a transformation to each element of the list and returns a new list with the transformed elements. The syntax for the List.Transform function is as follows:

List.Transform(list as list, transform as function) as list

Here, `list` is the list to be transformed, and `transform` is the function that will be applied to each element of the list. The `as list` at the end of the function definition is used to specify the output type of the function, which is also a list.

Examples of Using the List.Transform Function

Let's take a look at some examples of using the List.Transform function in Power Query.

Example 1: Converting All Text to Uppercase

Suppose we have a list of names that we want to convert to uppercase. We can use the List.Transform function to apply the `Text.Upper` function to each element of the list as follows:

let

names = {“john”, “jane”, “jim”},

uppercaseNames = List.Transform(names, each Text.Upper(_))

in

uppercaseNames

In this example, we define a list called `names` that contains three elements: john, jane, and jim. We then use the List.Transform function to apply the `Text.Upper` function to each element of the `names` list, which converts all text to uppercase. The resulting list is stored in the `uppercaseNames` variable.

Example 2: Extracting the Date from a List of Date-Times

Suppose we have a list of date-time values, and we want to extract only the date portion of each value. We can use the List.Transform function to apply the `DateTime.Date` function to each element of the list as follows:

let

dates = {#datetime(2021, 1, 1, 0, 0, 0), #datetime(2021, 1, 2, 0, 0, 0), #datetime(2021, 1, 3, 0, 0, 0)},

dateList = List.Transform(dates, each DateTime.Date(_))

in

dateList

In this example, we define a list called `dates` that contains three date-time values. We then use the List.Transform function to apply the `DateTime.Date` function to each element of the `dates` list, which extracts only the date portion of each value. The resulting list is stored in the `dateList` variable.

The List.Transform function is a powerful tool in Power Query that allows users to apply a transformation to each element of a list. By understanding the M code behind this function, users can better leverage its power and flexibility to transform data in a variety of ways. In this article, we explored the syntax of the List.Transform function and provided examples of how it can be used to perform common data transformations.

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