title: Selecting Max Column Values in R
body: <p>I'm pretty new to R and have a question regarding selecting the max values in a column.</p>
  
  <p>I have the following data frame:</p>
  
  <pre><code>          X      Y
   [1,]     1     10
   [2,]     1     12
   [3,]     1     NA
   [4,]     2     5
   [5,]     2     6
   [6,]     2     7
   [7,]     2     8
   [8,]     3     NA
   [9,]     3     NA
  [10,]     3     1
  </code></pre>
  
  <p>I would like to select the max value of column Y and replace all values of Y within each group with that value.  My output data frame would look like this:</p>
  
  <pre><code>          X      Y
   [1,]     1     12
   [2,]     1     12
   [3,]     1     12
   [4,]     2     8
   [5,]     2     8
   [6,]     2     8
   [7,]     2     8
   [8,]     3     1
   [9,]     3     1
  [10,]     3     1
  </code></pre>
  
  <p>Any help would be appreciated.  Thanks!</p>
  
  <p>Here's the data</p>
  
  <pre><code>Data &lt;- structure(list(X = c(1L, 1L, 1L, 2L, 2L, 2L, 2L, 3L, 3L, 3L), 
                       Y = c(10L, 12L, NA, 5L, 6L, 7L, 8L, NA, NA, 1L)), 
                  .Names = c("X", "Y"), class = "data.frame",
                  row.names = c("[1,]", "[2,]", "[3,]", "[4,]", "[5,]", "[6,]", "[7,]", "[8,]", "[9,]", "[10,]"))
  </code></pre>