Why can't one read and write both csv's?

[josiekre]

I see in the help that writing to csv isn't allowed if reading from one (when using as a script). What is the reason for this? This is exactly what I was hoping to do. :)

I think I could facilitate this on my own by writing a python script to read my data first, use tzwhere internally, and then writing a csv. But I'm guessing that I'm missing something here otherwise you'd have implemented this.

[cstich]

The import/export options of the script are mainly there to convert between different types of input files if you want to do that, so it doesn't make a lot of sense to go from CSV to CSV file. The script options are not particularly useful from an end-user perspective, but they make it relatively painless to ship with the most up-to-date version of the timezone map (which reminds me that I have to update that), and see whether you broke anything before you commit.

I am not a 100% sure I understand what you exactly want to do, but if you could elaborate a bit that would be great. I feel like I am now the one that is missing something obvious :)

You don't want to export polygons with timezone information by any chance?

[josiekre]

I simply need an offline way to append local time to a csv file with
lat/lon/timestamp (UTC). (Actually in my case it's a bunch of csv files at
once so I use glob.) I am doing analysis in R, and so in/out csv means I
can call it from R with 'system(python tzwhere.py)' and then call
'read_csv()" again easily to get the results back in. I've done a quick and
dirty implementation like so:

from tzwhere import tzwhere
import glob
import pandas as pd

def reader(f):
  d = pd.read_csv(f, names=['id', 'latitude', 'longitude', 'timestamp'])
  return d


def main():
  files = glob.glob('*.csv')
  data = pd.concat([reader(f) for f in files], ignore_index=True)
  tz = tzwhere.tzwhere(shapely=True)
  data['local_tz'] = data.apply(lambda row: tz.tzNameAt(row['latitude'],
                                                row['longitude']), axis=1)

  data.to_csv('to_r.csv', index=False)

if __name__ == "__main__":
  main()

---------- Forwarded message ----------
From: cstich notifications@github.com
Date: Tue, Nov 17, 2015 at 6:34 PM
Subject: Re: [pytzwhere] Why can't one read and write both csv's? (#30)
To: pegler/pytzwhere pytzwhere@noreply.github.com
Cc: Josie Kressner josie@transportfoundry.com

The import/export options of the script are mainly there to convert between
different types of input files if you want to do that, so it doesn't make a
lot of sense to go from CSV to CSV file. The script options are not
particularly useful from an end-user perspective, but they make it
relatively painless to ship with the most up-to-date version of the
timezone map (which reminds me that I have to update that), and see whether
you broke anything before you commit.

I am not a 100% sure I understand what you exactly want to do, but if you
could elaborate a bit that would be great. I feel like I am now the one
that is missing something obvious :)

You don't want to export polygons with timezone information by any chance?

—
Reply to this email directly or view it on GitHub
#30 (comment).

[cstich]

Your code makes sense to me as it is. Pandas is probably a much better choice for doing all the reading and writing of CSV files than using anything in pytzwhere for that. Does that answer your original question?

[josiekre]

Sure thing. I'll continue to use the script with pandas.