title: Has parquet file the size greater csv in string data?
body: <p>I have a csv with the size equal to 170kB, and when I convert them to the parquet file, the size is 1.2MB. The data structure is 12 columns with strings.</p>
  
  <pre class="lang-py prettyprint-override"><code>import pandas as pd
  import pyarrow as pa
  import pyarrow.parquet as pq
  
  csv_filename = "../files/test.csv"
  parquet_filename = '../files/sample.parquet'
  chunksize = 1
  pqwriter = None
  for i, df in enumerate(pd.read_csv(csv_filename, delimiter='_;_', chunksize=chunksize)):
      #df = df.astype(str)
      table = pa.Table.from_pandas(df=df)
      # for the first chunk of records
      if i == 0:
          # create a parquet write object giving it an output file
          pqwriter = pq.ParquetWriter(parquet_filename, table.schema, compression='gzip', use_dictionary=False)
      pqwriter.write_table(table)
  
  # close the parquet writer
  if pqwriter:
      pqwriter.close()
  
  df = pd.read_parquet(parquet_filename)
  print(df.memory_usage(deep=True))
  </code></pre>
  
  <p>Update 1:
  I tried with <code>fastparquet</code> and I got 933kB in size.</p>
  
  <pre class="lang-py prettyprint-override"><code>for i, df in enumerate(pd.read_csv(csv_filename, delimiter='_;_', chunksize=chunksize)):
      fastparquet.write(parquet_filename, df, compression='gzip', append=True)
  </code></pre>
  
  <p>Update 2:
  The parameter <code>chunksize</code> have impact in file size. If larger, the size decreases. Using <code>chunksize</code> equal 30, the size was 76kB.</p>