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POSubtly different behaviour between with() and attach() in R?
 

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  1. POSubtly different behaviour between with() and attach() in R?
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    <p>People often use the <code>attach()</code> and <code>detach()</code> functions to set up "search paths" for variable names in R, but because this alters global state that's hard to keep track of, <a href="https://stackoverflow.com/questions/1310247/in-r-do-you-use-attach-or-call-variables-by-name-or-slicing/1311620#1311620">people</a> recommend <a href="https://stackoverflow.com/questions/5797797/attach-inside-function/5800785#5800785">using <code>with()</code> instead</a>, which sets up a temporary alteration to the search path for the duration of a single expression.</p> <p>However I just noticed that unlike <code>attach()</code>, <strong><code>with()</code> apparently doesn't "resolve through" functions</strong>. For example, let's first set up a dummy function that will access a variable named <code>x</code>:</p> <pre><code>f &lt;- function { print(x) } </code></pre> <p>Now,</p> <pre><code>with(list(x=42), f()) </code></pre> <p>fails even though</p> <pre><code>with(list(x=42), print(x)) </code></pre> <p>and</p> <pre><code>attach(list(x=42)) f() </code></pre> <p>both succeed! :(</p> <p>Can anyone tell me why? I would like <code>with()</code> to behave exactly like <code>attach()</code> does here, to enable me to effectively pass a big parameter list to a function by setting up an environment containing the parameter values with <code>with()</code>. I see this approach as having several benefits over the alternatives (the two I've considered are (a) laboriously passing all the parameters into the function, and (b) explicitly passing in a list/frame of parameters as a function argument and having the function itself call <code>with()</code>), but it doesn't work. I find this discrepancy pretty troubling to be honest! Any explanation/help would be appreciated.</p> <p>I'm using R 2.11.1.</p>
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