Extracting unique values from data frame using R
<p>I have a data frame with multiple columns and I want to be able to isolate two of the columns and get the total amount of unique values... here's an example of what I mean:</p>

<p>Lets say i have a data frame df:</p>

<pre><code>df&lt;- data.frame(v1 = c(1, 2, 3, 2, "a"), v2 = c("a", 2 ,"b","b", 4))
df

  v1 v2
1  1  a
2  2  2
3  3  b
4  2  b
5  a  4
</code></pre>

<p>Now what Im trying to do is extract just the unique values over the two columns. So if i just used unique() for each column the out put would look like this:</p>

<pre><code>&gt; unique(df[,1])
[1] 1 2 3 a
&gt; unique(df[,2])
[1] a 2 b 4
</code></pre>

<p>But this is no good as it only finds the unique values per column, whereas I need the total amount of unique values over the two columns! For instance, 'a' is repeated in both columns, but I only want it counted once. For an example output of what I need; imagine the columns V1 and V2 are placed on top of each other like so:</p>

<pre><code>  V1_V2
1      1
2      2
3      3
4      2
5      a
6      a
7      2
8      b
9      b
10     4
</code></pre>

<p>The unique values of V1_V2 would be:</p>

<pre><code>   V1_V2
1      1
2      2
3      3
5      a
8      b
10     4
</code></pre>

<p>Then I could just count the rows using nrow().
Any ideas how I'd achieve this?</p>