Attribute to value, assign attribute's value to a new attribute

I have a list of features. Each has a number of columns with a date as name and as value a numeric value. I want to use the date columns as a new column's attribute value, and write the date column's value into another field, like this:

In this example I'd end up with 3 features. Furthest I've gotten so far was with the AttributeTransposer, however it returns every other field's value as missing and I can't get them back. Any ideas how to accomplish this?