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2013-05-15T15:34:59.943
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2013-05-15T15:34:59.943
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<p>This problem bothered me for months now. Today I found a very handy solution inspired by <a href="https://stat.ethz.ch/pipermail/r-help/2012-January/299743.html" rel="nofollow">https://stat.ethz.ch/pipermail/r-help/2012-January/299743.html</a></p> <p>Let's start with a ReferenceClass which has an erroneous implementation:</p> <pre><code>MyClass <- setRefClass( "MyClass", fields = list( xy = "data.frame" ), methods = list( initialize = function( df ){ if( !missing( df ) ){ xy <<- df } }, getSecondRow = function(){ # A mistake happend here return( xy[1,] ) } ) ) mc <- MyClass$new( data.frame( a = 1:10, b = rnorm(10) ) ) mc$getSecondRow() a b 1 1 0.1349983 </code></pre> <p>The implementation of <code>getSecondRow</code> does obviously not provide the desired result. So the fixed method should actually look like</p> <pre><code> getSecondRow = function(){ return( xy[2,] ) } </code></pre> <h2>Classes without explicit implementation of the constructor</h2> <p>The trick instead of loading the class and reproducing the object from scratch is to construct an new object from the existing, using the copy constructor functionality of the default <code>initialize( ... )</code> constructor. After debugging and reloading the class you can just copy the existing object with the implementation into the same variable by</p> <pre><code># NOTRUN mc <- MyClass$new( mc ) </code></pre> <h2>Classes with overwritten constructor.</h2> <p>However, in the case presented here, the standard constructor is already overwritten. But in such cases you can simply use the functionality of <code>callSuper( ... )</code> such that your constructor should look like</p> <pre><code> initialize = function( df, ... ){ callSuper( ... ) if( !missing( df ) ){ xy <<- df } } </code></pre> <p>Finally, your fixed object is derived by</p> <pre><code>mc <- MyClass$new( mc$xy, mc ) mc$getSecondRow() a b 2 2 0.8452587 </code></pre>
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