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<p>Say you use the base #rstats <code>lm()</code> command</p>
<p><code>lm(data=dat_foo[,c('y','x1','x2')],y ~ x1 + x2 + x1:x2)</code></p>
<p>I want to be able to map the single formula term <code>x1:x2</code> to the two<br>
‘generating’ columns  <code>dat_foo[,c('x1','x2')]</code></p>
<p>In words, for a term in a <code>?formula</code>, lookup the involved ‘root’ columns of the data frame inside the formula’s associated environment.</p>
<p>I feel like this mapping must exist under the <code>lm()</code> hood somewhere. Various stackoverflow Q+A’s about formulas never directly talk about this lookup. This <a target="_blank" rel="nofollow" href="https://www.rstudio.com/rviews/2017/02/01/the-r-formula-method-the-good-parts/">Rviews blog post</a> sums up the formula landscape pretty well. But there does not seem to be a convenient expose of the explicit lookup/hash table of the df to term mapping.</p>
<p>I have to hand roll the few lines of code to implement the hash / lookup table myself. My solution is ‘loose’ since it chops up the terms in the formula, then creates many sub-formulas for each chopped term.</p>
<p>Is there a better / preferred way?</p>
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