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POR ddply, applying if and ifelse functions
 

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  1. POR ddply, applying if and ifelse functions
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    <p>I'm trying to apply a function to a dataframe using ddply from the plyr package, but I'm getting some results that I don't understand. I have 3 questions about the results </p> <p>Given:</p> <pre><code>mydf&lt;- data.frame(c(12,34,9,3,22,55),c(1,2,1,1,2,2) , c(0,1,2,1,1,2)) colnames(mydf)[1] &lt;- 'n' colnames(mydf)[2] &lt;- 'x' colnames(mydf)[3] &lt;- 'x1' </code></pre> <p>mydf looks like this:</p> <pre><code> n x x1 1 12 1 0 2 34 2 1 3 9 1 2 4 3 1 1 5 22 2 1 6 55 2 2 </code></pre> <h3>Question #1</h3> <p>If I do:</p> <pre><code>k &lt;- function(x) { mydf$z &lt;- ifelse(x == 1, 0, mydf$n) return (mydf) } mydf &lt;- ddply(mydf, c("x") , .fun = k, .inform = TRUE) </code></pre> <p>I get the following error:</p> <pre><code>Error in `$&lt;-.data.frame`(`*tmp*`, "z", value = structure(c(12, 34, 9, : replacement has 3 rows, data has 6 Error: with piece 1: n x x1 1 12 1 0 2 9 1 2 3 3 1 1 </code></pre> <p>I get this error regardless of whether I specify the variable to split by as c("x"), "x", or .(x). I don't understand why I'm getting this error message.</p> <h3>Question #2</h3> <p>But, what I really want to do is set up an if/else function because my dataset has variables x1, x2, x3, and x4 and I want to take those variables into account as well. But when I try something simple such as:</p> <pre><code>j &lt;- function(x) { if(x == 1){ mydf$z &lt;- 0 } else { mydf$z &lt;- mydf$n } return(mydf) } mydf &lt;- ddply(mydf, x, .fun = j, .inform = TRUE) </code></pre> <p>I get:</p> <pre><code>Warning messages: 1: In if (x == 1) { : the condition has length &gt; 1 and only the first element will be used 2: In if (x == 1) { : the condition has length &gt; 1 and only the first element will be used </code></pre> <h3>Question #3</h3> <p>I'm confused about to use function() and when to use function(x). Using function() for either j() or k() gives me a different error:</p> <pre><code>Error in .fun(piece, ...) : unused argument (piece) Error: with piece 1: n x x1 z 1 12 1 0 12 2 9 1 2 9 3 3 1 1 3 4 12 1 0 12 5 9 1 2 9 6 3 1 1 3 7 12 1 0 12 8 9 1 2 9 9 3 1 1 3 10 12 1 0 12 11 9 1 2 9 12 3 1 1 3 </code></pre> <p>where column z is not correct. Yet I see a lot of functions written as function().</p> <p>I sincerely appreciate any comments that can help me out with this</p>
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    1. CO@Metrics Both questions involve ddply and ifelse, but in what sense other than that could they be considered duplicates?
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    2. CO@Joran: other than these two, none :)
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    3. CO+1 for reproducible example and clear explanation
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      1. USSimon O'Hanlon
 

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