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POHow to join (merge) data frames (inner, outer, left, right)?
 

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  1. POHow to join (merge) data frames (inner, outer, left, right)?
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    <p>Given two data frames:</p> <pre><code>df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3))) df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1))) df1 # CustomerId Product # 1 Toaster # 2 Toaster # 3 Toaster # 4 Radio # 5 Radio # 6 Radio df2 # CustomerId State # 2 Alabama # 4 Alabama # 6 Ohio </code></pre> <p>How can I do database style, i.e., <a href="http://en.wikipedia.org/wiki/Join_%28SQL%29" rel="noreferrer">sql style, joins</a>? That is, how do I get:</p> <ul> <li>An <a href="http://en.wikipedia.org/wiki/Join_%28SQL%29#Inner_join" rel="noreferrer">inner join</a> of <code>df1</code> and <code>df2</code>:<br> Return only the rows in which the left table have matching keys in the right table.</li> <li>An <a href="http://en.wikipedia.org/wiki/Join_%28SQL%29#Outer_join" rel="noreferrer">outer join</a> of <code>df1</code> and <code>df2</code>:<br> Returns all rows from both tables, join records from the left which have matching keys in the right table.</li> <li>A <a href="http://en.wikipedia.org/wiki/Join_%28SQL%29#Left_outer_join" rel="noreferrer">left outer join (or simply left join)</a> of <code>df1</code> and <code>df2</code><br> Return all rows from the left table, and any rows with matching keys from the right table.</li> <li>A <a href="http://en.wikipedia.org/wiki/Join_%28SQL%29#Right_outer_join" rel="noreferrer">right outer join</a> of <code>df1</code> and <code>df2</code><br> Return all rows from the right table, and any rows with matching keys from the left table.</li> </ul> <p>Extra credit:</p> <p>How can I do a SQL style select statement?</p>
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