Variable column formula

[greyangel23]

I have to cells labeled Month1 and month 2. Month 1 and month 2 are columns in my power query. What I need to do is create a custom column that subtracts month 1 from month 2, however I do not know how to make the column names variable in M code. Below is what I want to happen but obviously this isn't working.
= Table.AddColumn(#"Changed Type", "Custom", each [Month2]-[Month1])

 

[Matt Allington]

Use the menus. That’s what they’re for. Go to Add/Add column/custom column. Write
[Month2]-[Month1]
In the dialogue box

 

[greyangel23]

Does not work because Month2 and Month1 are variable names. Example I have a table that is called Month2 which equals August and a table called Month1 which equals July. I can't use July and August because this custom column can change every month depending on what the user types into these tables

 

[Matt Allington]

You said Month 1 and Month 2 are columns. My solution works in that instance. How about you post some realistic sample data and illustrate what you are trying to do with it and then someone can no doubt help you.

 

[IR15H]

First, rename your variable column names by referring to their position - to be able to 'consistently' name them;

= Table.RenameColumns(#"Changed Type",{{Table.ColumnNames(#"Changed Type"){0}, "[Month 2]"}, {Table.ColumnNames(#"Changed Type"){1}, "[Month 1]"}})

Replace 0 and 1 with where your Month columns appear in your query (with your first column being 0, the second 1, and so on).

After than, you can do your [Month 2] - [Month 1] step, as they'll then always be called that.