How to get the reference level of a factor column?

Asked Jun 14 '22 at 21:13

Active Jun 14 '22 at 21:13

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I know you can use relevel to set a value as the reference level of a factor.

I want to do the opposite: given a factor column, how can I retrieve the reference value?

I guess the most trivial way would be to run a regression with lm and see which value is missing from the estimated coefficients.

Is there a method/function for this?

I feel silly asking this, but searching how to retrieve the reference level of a factor results in tons of questions asking how to relevel a factor (such as this one). I couldn't find anything on how to do the opposite, so I apologize in advance in case this is a duplicate!

asked Jun 14 '22 at 21:13

Arturo Sbr

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The reference is the first level of the factor, so you can just use `levels(x)[1]`. – Ritchie Sacramento Jun 14 '22 at 21:17
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That's great. Thanks! Does this hold after releveling a column? If so, do you want to post it as an answer and I'll accept it? – Arturo Sbr Jun 14 '22 at 21:25
@RitchieSacramento, please post as answer. – Ben Bolker Jun 15 '22 at 00:16

How to get the reference level of a factor column?

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