Sum a column based on condition in another column in R
<p>I have a dataset with 150+ columns and 1000s of rows. The dataset provides a flag for different items for various categories in different columns. One of the columns is total usage for each item across the category. Below is sample of the dataset:</p>

<pre><code>Values   A B C
1        Y   
2          Y
3        Y   Y 
4            Y 
</code></pre>

<p>I want to use R to do calculations such that I get the following results:</p>

<pre><code>     Count  Sum
A      2     4
B      1     2
C      2     7
</code></pre>

<p>Basically I want the Count Column to give me the number of "y" for A, B and C, and the Sum column to give me sum from the Usage column for each time there is a "Y" in Columns A, B and C</p>

<p>Step 2 -  I have similar column values in 200 + files. I have brought all the files into a folder. What I would like to do is use the above functions, apply it in each of the file, and then have the answer grouped by file and category. for example</p>

<p><code>File 1 Count A Sum A Count B Sum B Count C Sum C</code></p>

<p><code>File 2 Count A Sum A Count B Sum B Count C Sum C</code></p>

<p>and so on</p>