Power Query: Data Transformation of Dynamic Columns

When you manually select all columns and apply a transformation (for example, changing the data type) the generated code lists each column name individually – it looks something like this:

// Generated code from manual actions
=   Table.TransformColumnTypes ( 
        #"Previous Step",
            {"First Column", type text}, 
            {"2nd Column", type text}, 
            {"Col 3", type text}, 
            {"COLUMN FOUR", type text}, 
            {"Number Five (is alive)", type text}, 
            {"666", type text}

I frequently import data from files with varying column names, and / or varying numbers of columns. This makes it impossible to effectively hard code data transformations by column name – if somebody renames any of those columns, then the step above will fail.

So, instead of the generated steps to change each column type, we can use the List.Transform function to apply a transformation to each Column:

//Change All Columns to text
=   Table.TransformColumnTypes ( 
        #"Previous Step", 
        List.Transform ( 
            Table.ColumnNames ( #"Previous Step" ), 
            each {_, type text}

This example is about as simple as it gets – you can of course apply a broad range of transformation functions in this way – for example, Text.Trim:

//Trim All Columns
=   Table.TransformColumns ( 
        #"Previous Step", 
        List.Transform ( 
            Table.ColumnNames ( #"Previous Step" ), 
            each {_, Text.Trim, type text}

How to Unpivot Excel Data

All too often, data gets stored in crosstab format in Excel. Whilst crosstabs can be great for presenting data, they’re pretty poor for storing it, as it makes it tricky to manipulate the data. Therefore we often have a requirement to ‘unpivot’, or normalise the data. This is a quick tutorial of one method to unpivot Excel data.

Here’s an example of what we’re working with. This is some meaningless, imaginary data, showing some values grouped in a crosstab by colour columns, and by date rows:

Unpivot Excel data - raw crosstab data

Whilst this seems like a reasonable way to store the information, it actually makes it pretty difficult to answer questions about this data – for example, what percentage of September values were Red?

What we really want is for each row to contain only one value, and for colour to be a column field. Then we can easily use a pivot table to interrogate this data.

We’re going to use a Multiple Consolidation Range pivot table to do the hard work for us.

1. Start off by pressing keys ALT > D > P to open the Pivot Table Wizard dialog box:

Unpivot Excel data - Pivot Wizard Step 1

Choose the ‘Multiple consolidation ranges’ option, then click ‘Next’

2a. In step 2a of the wizard, choose the ‘I will create the page fields’ option, and click ‘Next’

Unpivot Excel data - Pivot WIzard Step 2a


2b. Now we need to add our crosstab data range as a data source for this pivot table. Enter / select the appropriate range, then click ‘Add’. Then click ‘Next’.

Unpivot Excel data - Pivot Wizard Step 2b


3. Choose a location for the intermediate pivot table (it’s a good idea to use a new worksheet, as we can simply delete the entire worksheet when we’re finished). Then click ‘Finish’.

Unpivot Excel data - Pivot Wizard Step 3


4. We now have an ‘intermediate’ pivot table, which looks very similar to our raw data, but has some grand totals. Now we want to drill into the source data for this pivot table, by double clicking on the overall Grand Total value – the cell intersection of the Grand Total column, and Grand Total row – circled red:

Unpivot Excel data - Intermediate pivot table


5. By double clicking to drill into the grand total data source, another worksheet is created, containing a table with our unpivotted data:

Unpivot Excel data - Unpivotted data

You can see that we now have colour as a column field, rather than four separate column headings – which allows us to use this data as a field in a pivot table report.

So, returning to our original example question – what percentage of September values were red? – it is now easy to put a quick pivot table together to answer this:

Unpivot Excel data - Pivot table report output

This is one method to unpivot Excel Data, which works well for simple crosstabs. It won’t deal with all cases – for example, where you already have multiple row fields in your data – but for simple cases like this example dataset, it’s a really quick and easy way of making your data a bit more accessible.

Download Excel file Download Example Workbook