title: left_join function between x and y data frames returns more rows than the first data frame in r
body: <p>I have two data frames with the following dimension: </p>
  
  <pre><code>dim(x)
  8637   133
  
  dim (y)
  8113   26 
  </code></pre>
  
  <p>I am trying to merge x and y by one common column in x and y. I am using left_join function from dplyr package. </p>
  
  <pre><code>df &lt;- dplyr::left_join(x, y, by = "col1")
  </code></pre>
  
  <p>The number of rows in the merged data is more than the first data frame(x). </p>
  
  <pre><code>nrow(df)
  8666
  </code></pre>
  
  <p>What I would expect to get after merging x and y is a new data frame with all rows from x as well as all columns from both x and y. I guess this is what left_join in dplyr is supposed to do but there is something wrong in the result of left_join(). Any idea how I can fix the issue?   </p>