Posts in Category ‘M’

Trimming text with custom characters in Power BI and Power Query

When cleaning dirty data, you might have used the Trim-function (Text.TrimStart or Text.TrimEnd) to delete leading or trailing whitespace from your strings. However, did you know that you could use these functions as well to delete any other characters as well from the start or end of a string? Trimming text with custom characters is pretty straightforward:

Task: Trimming text with custom characters

Say you have a column with values like so

Trimming text with custom characters

and want to delete every number at the end and also every “-” that is directly connected with a number. So that the final output shall look like so:

Trim custom characters at the end of a string.

Optional parameter

By default, you feed just one argument into the Text.TrimStart or Text.TrimEnd function: The string whose whitespace characters shall be removed.

Text.TrimEnd(text as nullable text, optional trim as any) as nullable text

But the second argument lets you define a list of your own characters to be removed respectively. So I can create a list with all the characters that shall be removed from the end like so:

{"0".."9"} & {"-"}

This concatenates 2 lists: The first list contains 10 elements: All numbers as strings. The second list has just one element in it: “-“. I have to put this element into a list as well for being able to use the ampersand (“&”) as an easy concatenator here.

So the full expression for the “Add custom column” dialogue looks like so:

Text.TrimEnd( [MyColumnName], {"0".."9"} & {"-"} )

To see this in action, you can simply paste this code into the advanced editor and follow the steps:

Enjoy and stay queryious 😉

Date.Networkdays function for Power Query and Power BI

Today I’m going to share my custom NETWORKDAYS function for Power Query with you that uses the same syntax than its Excel-equivalent.

NETWORKDAYS function

This function’s first 3 parameters work just like the Excel function and there is a 4th parameter that allows adjusting the day on which the week shall start:

  1. Start as date
  2. End as date
  3. optional holidays as list of dates
  4. optional number to change the start of the week from Monday (default: 1) to any other day (2 would mean that the week starts on Tuesday instead)

The function comes with a UI that lets you first choose a table containing the holidays and then choose the column with the holiday dates. Read more

Tidy up Power BI models with the Power BI Cleaner tool

Edit 23th June 2020: Updated version (see download link at the end of the article) to reflect changes with the vpax fileformat in DAX Studio versions V11.0 upwards.

The VertiPaq-Analyzer tool is one of the great community tools that I really cannot live without. It gives me a great overview of all elements in my model and identifies potential performance problems by showing the storage requirements of each column. So when seeing expensive columns, the first question that arises is: “Do I really need this column or could I delete it?”. Luckily, this can now be answered with my new Power BI Cleaner tool. This tool shows the usage of all columns (and measures) within the tables of the VertiPaq Analyzer.

Power BI Cleaner shows unused columns in the VertiPaq-tables

Power BI Cleaner tool

So whenever there is no entry in the column “Where Used” you can go ahead and eliminate the column (or measure) from the model. Well – with two exception actually: Fields used in the definition of incremental load policies are currently not identified as well as used fields in calculation groups. So make sure to consider this before running wild 😉 Read more

Advanced transformations on multiple columns at once in Power BI and Power Query

You can apply simple transformations to multiple columns at once in Power Query using the UI only. In this article I show how you can apply advanced transformations on multiple columns at once instead. You can also use this to use custom functions instead. And lastly for the lazyefficient fans of custom M-functions: You will get a new “TranformAllMyColumnsAtOnceHowILikeIt”-function as well 😉

Background

The Transform-tab in the query editor is sensitive to the columns you select. So if you select multiple number columns for example, some number transformations will be greyed out and are therefore not accessible:

Some symbols are greyed out, Advanced transformations on multiple columns at once in Power BI and Power Query, Power BI, Power Query, Power BI Desktop

Some symbols are greyed out

So how could I then multiply all my columns by 10 for example, as the symbol for multiplication is greyed out? Read more

Dynamically create types from text with Type.FromText in Power Query and Power BI

In this article I’ll show you how to create types from text in Power Query, enabling you to dynamically change types via functions for example. It’ll come out as a custom Type.FromText function which has been asked for in the comments of this article: https://www.thebiccountant.com/2017/01/09/dynamic-bulk-type-transformation-in-power-query-power-bi-and-m.

Problem

To transform a column to type text can be done like so:

Table.TransformColumnTypes(Source,{{"Column1", type text}})

This transforms the “Column1” from table “Source” to type text.  Now, if you want to make the type dynamic and move it to a function parameter like so:

(VariableType as type) =>

Table.TransformColumnTypes(Source,{{"Column1", VariableType}})

This returns a function dialogue as follows:

Read more

Performance tip for aggregations after joins in Power Query and Power BI

This article was edited on 2nd Nov 2019. JoinKind.Local has been removed to avoid problems with merges on tables with primary keys:

In this article you’ll learn how to speed up the aggregation of joined/merged tables by orders of magnitude (I recorded up to 30 times faster execution times). This method works for merges where both table have multiple rows for each keys. If one of your tables has a primary key, the method Chris Webb describes here works just as good: Chris Webb’s article on how to improve performance on aggregations after joins using primary keys .

You can follow along the different methods in this file:  PerformanceAggregationsAfterMerges1_Upload.zip

Background

When you join a table to another table in Power Query, the UI gives you the option to either expand the columns (default) or aggregate the contents of the joint tables. That’s useful if multiple rows are returned for the rows of the table that has been joined to (left table):

Read more