A Power Query Custom Function to Rename all Columns at Once in a Table

A Power Query Custom Function to Rename all Columns at Once in a Table

I am involved with a Power BI development in the past few days. I got some data exported from various systems in different formats, including Excel, CSV and OData. The CSV files are data export dumps from an ERP system. Working with ERP systems can be very time consuming, especially when you don’t have access to the data model, and you get the data in raw format in CSV files. It is challenging, as in the ERP systems, the table names and column names are not user friendly at all, which makes sense. The ERP systems are being used in various environments for many different customers with different requirements. So if we can get our hands to the underlying data model, we see configuration tables keeping column names. Some of the columns are custom built to cover specific needs. The tables may have many columns that are not necessarily useful for analytical purposes. So it is quite critical to have a good understanding of the underlying entity model. Anyhow, I don’t want to go off-topic.

The Problem

So, here is my scenario. I received about 10 files, including 15 tables. Some tables are quite small, so I didn’t bother. But some of them are really wide like having between 150 to 208 columns. Nice!

Looking at the column names, they cannot be more difficult to read than they are, and I have multiple tables like that. So I have to rename those columns to something more readable, more on this side of the story later.


I emailed back to my customer, asking for their help. Luckily they have a very nice data expert who also understands their ERP system as well as the underlying entity model. I emailed him all the current column names and asked if he can provide more user-friendly names. He replied me back with a mapping table in Excel. Here is an example to show the Column Names Mapping table:

Column Names Mapping

I was quite happy with the mapping table. Now, the next step is to rename all columns is based on the mapping table. Ouch! I have almost 800 columns to rename. That is literally a pain in the neck, and it doesn’t sound quite right to burn the project time to rename 800 columns.

But wait, what about writing automating the rename process? Like writing a custom function to rename all columns at once? I recall I read an excellent blog post about renaming multiple columns in Power Query that Gilbert Quevauvilliers wrote in 2018. I definitely recommend looking at his blog post. So I must do something similar to what Gilbert did; creating a custom function that gets the original columns names and brings back the new names. Then I use the custom function in each table to rename the columns. Easy!

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Finding Minimum Date and Maximum Date Across All Tables in Power Query in Power BI and Excel

Finding Minimum Date and Maximum Date Across All Tables in Power Query in Power BI and Excel

When we talk about data analysis in Power BI, creating a Date table is inevitable. There are different methods to create a Date table either in DAX or in Power Query. In DAX you my use either CALENDAR() function or CALENDARAUTO() function to create the Date table. In Power Query you may use a combination of List.Dates()#date() and #duration() functions. Either way, there is one point that is always challenging and it is how to find out a proper date range, starting from a date in the past and ending with a date in the future, that covers all relevant dates within the data model. One simple answer is, we can ask the business. The SMEs know what the valid date range is..

While this is a correct argument it is not always the case. Especially with the Start Date which is a date in the past. In many cases the business says:

Lets’s have a look at the data to find out.

That is also a correct point, we can always a look at the data, find all columns with either Date or DateTime datatypes then sort the data in ascending or descending order to get the results. But what if there many of them? Then this process can be very time consuming.

Many of you may already thought that we can use CALENDARAUTO() in DAX and we are good to go. Well, that’s not quite right. In many cases there are some Date or DateTime columns that must not be considered in our Date dimension. Like Birth Date or Deceased Date. More on this later in this post.

In this post I share a piece of code I wrote for myself. I was in a situation to identify the Start Date and the End Date of the date dimension many times, so I thought it might help you as well.

How it works?

The Power Query expressions I share in this post starts with getting all existing queries using:

  • #sections intrinsic variable
  • Filtering out the current query name, which is GetMinMaxAllDates in my sample, to avoid getting the following error:

Expression.Error: A cyclic reference was encountered during evaluation.

Expression.Error: A cyclic reference was encountered during evaluation.
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