title: Create a table from the frequencies of taxa found in multiple CSV files
body: <p>I have 12 <code>.csv</code> files containing fetched taxonomic name and their frequencies (number of times each name was fetched). I've created a master <code>.txt</code> file listing all the unique taxa found at least once across the 12 files. I need to make a concatenated table in <code>csv</code> format where the headers of the rows are the name of each file, and the headers of the columns are all the unique taxa listed in the master <code>.txt</code> file. The table has to be populated with the frequencies next to each taxa in each <code>.csv</code> input file. Although the master list contains all taxa possible in the 12 files, not all files contain all the taxa. When the taxa is missing I need to place a '0'. </p>
  
  <p><code>.csv</code> input:</p>
  
  <pre><code>$cat file_1
  
  1,Salmo salar
  12,Solanum pennellii
  18,Staphylococcus xylosus
  ...
  
  $cat file_2
  
  1,Salmo salar
  14,Staphylococcus xylosus
  123,Strongyloides stercoralis
  ...
  
  $cat file_3
  
  123,Solanum pennellii
  11,Staphylococcus xylosus
  41,Strongyloides stercoralis
  ...
  </code></pre>
  
  <p><code>.txt</code> master list:</p>
  
  <pre><code>$cat master
  
  Salmo salar
  Solanum pennellii
  Staphylococcus xylosus
  Strongyloides stercoralis
  ...
  </code></pre>
  
  <p><code>.csv</code> output (what I need):</p>
  
  <pre><code>Sample,Salmo salar,Solanum pennellii,Staphylococcus xylosus,Strongyloides stercoralis
  File_1,1,12,18,0    
  File_2,1,0,14,123    
  File_3,0,123,11,41   
  </code></pre>
  
  <p>I previously tried making a small python script without a master list and using <code>.tsv</code> input files containing repeated names of taxa instead of frequencies. I wasn't able to obtain a table that showed missing taxa for each file, so I decided to create a master list and collapse the input files. I am very new at python, so any help will be appreciated.  </p>