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    <p>I <em>think</em> this is due to you not defining any arguments to <code>f</code>, and thence how the <code>x</code> required for <code>print(x)</code> is looked for.</p> <p>In normal use <code>f()</code> will look for <code>x</code> in the global environment if it isn't supplied (and it isn't nor can it be as <code>f</code> takes no arguments).</p> <p>Inside <code>with()</code>, what happens is that any arguments needed for <code>f</code> will be taken from the <code>data</code> argument. But because your <code>f</code> doesn't take any arguments, the <code>x</code> in the list is never used. Instead, R reverts to usual behaviour and looks up <code>x</code> in the environment of <code>f</code>, the global environment, and of course it isn't there. The difference with <code>attach()</code> is that it explicitly adds an object containing an <code>x</code> to the search path that is in the global environment.</p> <p>If you write your function properly, following the mantra that you pass in any and all arguments you use within the function, then everything works as one would expect:</p> <pre><code>&gt; F &lt;- function(x) print(x) &gt; with(list(x = 42), F(x)) [1] 42 &gt; ls() [1] "f" "F" </code></pre> <p>If you already have the list or arguments need for the call, perhaps consider <code>do.call()</code> to set up the call for you, instead of using with. For example:</p> <pre><code>&gt; do.call(F, list(x = 42)) [1] 42 </code></pre> <p>You still need your function to be properly defined with arguments, as your <code>f</code> doesn't work:</p> <pre><code>&gt; do.call(f, list(x = 42)) Error in function () : unused argument(s) (x = 42) </code></pre>
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    1. POSubtly different behaviour between with() and attach() in R?
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    1. USGavin Simpson
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    1. COThanks. I appreciate that there's risk in not specifying the arguments to `f`, but I thought this approach would be nice because `with(z, f())` allows `f()` to treat `z` a bit like an object of a class -- it can treat its values like member variables, with handy terse syntax to access them. `do.call()` is handy too, thanks, though I'll probably just use an explicit parameter to cut down on obfuscation.
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    2. CO@Gavin Simpson - I *know* your right :)
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    3. CO@Tommy That's good to know. Wish my wife said things like that ;-)
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