来自使用变量的现有的新data.frame（）不会带有列名

I want a shiny app to subset my dataframe based on user input. In this case, 'decision' is an input. I use a switch method to get the value of decision. I'm struggling with this because I can't get the colnames() method to work properly on a data frame that is created in a reactive function because the data frame becomes a function and doesn't have columns. As a solution, I'm trying to get the names set before I send it through a reactive function. However, the name of the column when I use a variable to determine which column to pull into my new df does not change, so the following functions are thrown off.I want a shiny app to subset my dataframe based