While it’s fairly common to need to load fixed-width files using Power Query or Power Query (and there’s a nice walkthrough of how to do this here), occasionally you might want to use Power Query and Excel to create a fixed-width output for another system, or maybe to create some test data. You might not want to do it often but I can imagine that when/if Power Query is integrated into SSIS this will be a slightly less obscure requirement; at the very least, this post should show you how to use a couple of M functions that are under-documented.
Before we begin, a quick tip: when working with any fixed width file always check the Monospaced box on the View tab in the Query Editor window, to make it easier to just the widths. You’ll notice I’ve done this in all the screenshots in this post.
For source data, let’s take the following expression which returns a table:
#table(
type table[Month=text,Product=text,Sales=text,Comments=text],
{
{"Jan","Apples","1","Not good"},
{"Feb","Pears","2","Better"},
{"March","Oranges","50000","Great!"}
})
Of course this could be any table of data that you choose, it’s just that using an expression like this makes the examples easier to follow. The only thing to notice here is that all the columns have a data type of text, even the Sales column: if your table doesn’t, I suggest you convert all the data types to text before you start – it will save you having to do it later.
The next thing you’ll need to do is to create a custom column that returns a list containing all the values from each of the columns from the current row. The expression to use here is:
Record.FieldValues(_)
For more information about what the underscore means here, see my previous post; basically it refers to the values in the current row.
Finally, you need to concatenate all the values in this list (which should all be text already, of course) into a single piece of fixed-width text. To do this we’ll need to use a Combiner function – a function that returns a function that, in turn, combines multiple pieces of text together in a specific way. I’ve already blogged about the Combiner.CombineTextByDelimiter() function here but in this case we’ll be using Combiner.CombineTextByRanges() which is a little more complex. You can’t use Combiner.CombineTextByRanges() to combine text directly, you have to call it to get a function that combines text in the way you want and then use this function on your data. To do this you need an expression like:
Combiner.CombineTextByRanges({{0,3},{9,10},{19,10},{29,255}})
How does this work? For each line, remember, we now have a value of type list that contains all of the values from the four columns in our table. The expression above returns a function that takes a list and constructs a single line of text from it. The list passed to the first parameter consists of a series of lists of two integers, and each value pair gives the position to place each value on the line and the number of characters to allow. So, in this example, the first value in the input list is put at position 0 on the line and is given a space of 3 characters; the second value in the input list is put at position 9 and given a space of 10 characters; the third value in the input list is put at position 19 and given a space of 10 characters; and the fourth value in the input list is put at position 29 and given a space of 255 characters.
This function can now be called in a second custom column to get the combined text for each line. Here’s the full M code for the query:
let
Source = #table(
type table
[Month=text,Product=text,Sales=text,Comments=text],
{
{"Jan","Apples","1","Not good"},
{"Feb","Pears","2","Better"},
{"March","Oranges","50000","Great!"}
}),
ListOfValues = Table.AddColumn(
Source,
"List Of Values",
each Record.FieldValues(_)),
MyCombinerFunction = Combiner.CombineTextByRanges({
{0,3},
{9,10},
{19,10},
{29,255}
}),
OutputColumn = Table.AddColumn(
ListOfValues,
"Output Column",
each MyCombinerFunction([List Of Values]))
in
OutputColumn
And here’s the output:
One thing to notice: on the third line, the month name March has been truncated to Mar because we only specified a space of three characters for the month name.
There’s an optional second parameter to Combiner.CombineTextByRanges() that also needs some explanation. By default, the function that Combiner.CombineTextByRanges() returns will place your text on an otherwise blank line. However you can get it to place your text on a line that contains other characters apart from blank space. For example, if you alter the MyCombinerFunction step in the query shown above to be:
MyCombinerFunction = Combiner.CombineTextByRanges({
{0,3},
{9,10},
{19,10},
{29,255}
}
,Text.Repeat("#",285)
),
You get:
The Text.Repeat() function, as used in the expression above, returns a piece of text with the # character repeated 285 times, and that piece of text is used as the ‘background’ on which the values are superimposed.
Of course, now you’ve got your desired output all you need to do to create a fixed width file is to remove all other columns apart from Output Column in your query, load your query to a table in the Excel worksheet, turn off the header row for the table by unchecking the Header Row option on the ribbon:
…and then save the workbook in a .txt file format.
You can download the sample workbook for this query here.
