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POWhy is `[` better than `subset`?
 

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  1. POWhy is `[` better than `subset`?
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    <p>When I need to filter a data.frame, i.e., extract rows that meet certain conditions, I prefer to use the <code>subset</code> function:</p> <pre><code>subset(airquality, Month == 8 &amp; Temp &gt; 90) </code></pre> <p>Rather than the <code>[</code> function:</p> <pre><code>airquality[airquality$Month == 8 &amp; airquality$Temp &gt; 90, ] </code></pre> <p>There are two main reasons for my preference:</p> <ol> <li><p>I find the code reads better, from left to right. Even people who know nothing about R could tell what the <code>subset</code> statement above is doing.</p></li> <li><p>Because columns can be referred to as variables in the <code>select</code> expression, I can save a few keystrokes. In my example above, I only had to type <code>airquality</code> once with <code>subset</code>, but three times with <code>[</code>.</p></li> </ol> <p>So I was living happy, using <code>subset</code> everywhere because it is shorter and reads better, even advocating its beauty to my fellow R coders. But yesterday my world broke apart. While reading the <code>subset</code> documentation, I notice this section:</p> <blockquote> <p>Warning</p> <p>This is a convenience function intended for use interactively. For programming it is better to use the standard subsetting functions like [, and in particular the non-standard evaluation of argument subset can have unanticipated consequences.</p> </blockquote> <p>Could someone help clarify what the authors mean?</p> <p>First, what do they mean by "<em>for use interactively</em>"? I know what an interactive session is, as opposed to a script run in BATCH mode but I don't see what difference it should make.</p> <p>Then, could you please explain "<em>the non-standard evaluation of argument subset</em>" and why it is dangerous, maybe provide an example?</p>
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    1. COIt is slightly less (but nut less than subset) to use with, `with(airquality, airquality[Month == 8 & Temp > 90, ])`
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      1. USTyler Rinker
    2. COThis thread discusses the `subset()` warning: http://r.789695.n4.nabble.com/Variable-passed-to-function-not-used-in-function-in-select-in-subset-tt872217.html
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    3. COYou might also have a look at Cirlces 8.2.31 and 8.2.32 of 'The R Inferno' http://www.burns-stat.com/pages/Tutor/R_inferno.pdf
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      1. USPatrick Burns
 

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