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copied!<p><code>x</code> is defined in the global environment, not in your function.</p> <p>If you try to modify a non-local object such as <code>x</code> in a function then R makes a copy of the object and modifies the copy so each time you run your anonymous function a copy of <code>x</code> is made and its ith component is set to 4. When the function exits the copy that was made disappears forever. The original <code>x</code> is not modified.</p> <p>If we were to write <code>x[i] <<- i</code> or if we were to write <code>x[i] <- 4; assign("x", x, .GlobalEnv)</code> then R would write it back. Another way to write it back would be to set <code>e</code>, say, to the environment that <code>x</code> is stored in and do this:</p> <pre><code>e <- environment() sapply(1:10, function(i) e$x[i] <- 4) </code></pre> <p>or possibly this:</p> <pre><code>sapply(1:10, function(i, e) e$x[i] <- 4, e = environment()) </code></pre> <p>Normally one does not write such code in R. Rather one produces the result as the output of the function like this:</p> <pre><code>x <- sapply(1:10, function(i) 4) </code></pre> <p>(Actually in this case one could write <code>x[] <- 4</code>.)</p> <p>ADDED:</p> <p>Using the <a href="http://r-proto.googlecode.com">proto package</a> one could do this where method <code>f</code> sets the ith component of the <code>x</code> property to 4.</p> <pre><code>library(proto) p <- proto(x = 1:10, f = function(., i) .$x[i] <- 4) for(i in seq_along(p$x)) p$f(i) p$x </code></pre> <p>ADDED:</p> <p>Added above another option in which we explicitly pass the environment that <code>x</code> is stored in.</p>

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