Center Expression on One Single Experimental Condition

Add a new column to `.data` named `scaled_ddct`. This new columns stores delta delta Ct scaled expression values.

scale_ddct(.data, ..., compare_var, center_on)

Arguments

.data	A `data.frame` produced by `read_fluidigm()` and normalized by `normalize()`. The columns required are: `sample_name`,`target_name` and `expression`.
...	the variables to split `.data` with. Must be a column of `.data`.
compare_var	the variable used to compare expression. Must be a column of `.data`
center_on	the value of `compare_var` that you want to set to 1 (i.e. the one that you want to center your data on)

Details

Since large scale qPCR experiments are often multivariated, think clearly which variable you want to use to compare your data and which variable you want to use to split them.

The first one goes to the `compare_var` parameter, the others go to the tidy dots.