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POCoefficient Variable Membership in R
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2013-03-06T22:40:48.793
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2013-03-11T05:00:19.697
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2013-03-07T19:06:39.920
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I have worked up a horribly lengthy solution to this before using regular expressions but I hope there is a more native way to do it. Given a model, perhaps like <pre><code>data(tips, package="reshape2") mod <- lm(tip ~ total_bill*sex + sex*day, tips) mod$coefficients </code></pre> I want to identify which coefficients go with which variable in the formula. Like this: <pre><code>| Coefficient | Variable | |:-------------------|:---------------| | total_bill | total_bill | | sexMale | sex | | daySat | day | | daySun | day | | dayThur | day | | total_bill:sexMale | total_bill,sex | | sexMale:daySat | sex,day | | sexMale:daySun | sex,day | | sexMale:dayThur | sex,day | </code></pre> I have inspected <code>model.matrix</code> and <code>model.formula</code> but those led me to this line of code <pre><code>.Internal(model.matrix(t, data)) </code></pre> I dove into the C code but I figured there had to be an easier way. Is there? In response to DWin's nice answer I have built a convoluted example where the the regex could fail. This is one of those edge cases where regex scares me. The <code>data.frame</code> is built with variable names and values that can easily be confused which happens a lot. <pre><code>baseball <- data.frame(Bat=sample(1:100, 20, replace=T), Batter=sample(c("David", "Batley", "Bob", "Ace"), 20, replace=T), Hits=sample(1:20, 20, replace=T)) baseball bMod <- lm(Hits ~ Bat*Batter, baseball) bMod$coefficients col.matx <- sapply(colnames(model.matrix(bMod)), function(cols) sapply(labels(bMod), function(trm) grep(patt=trm, x=cols, value=TRUE))) </code></pre> This matches the continuous variable <code>Bat</code> to all the coefficients for the <code>factor</code> <code>Batter</code>. Yes, this is a stupid example, but can easily happen.
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<r><names><lm><model.matrix>
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Coefficient Variable Membership in R
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