The fastest way to parse dates in Python when reading .csv file?

Question

I have a .csv file that has 2 separate columns for 'Date' and ' Time'. I read the file like this:

data1 = pd.read_csv('filename.csv', parse_dates=['Date', 'Time'])

But it seems that only the ' Date' column is in time format while the 'Time' column is still string or in a format other than time format.

When I do the following:

data0 = pd.read_csv('filename.csv')
data0['Date'] = pd.to_datetime(data0['Date'])
data0['Time'] = pd.to_datetime(data0['Time'])

It gives a dataframe I want, but takes quite some time. So what's the fastest way to read in the file and convert the date and time from a string format?

The .csv file is like this:

              Date      Time      Open       High       Low     Close  
0       2004-04-12    8:31 AM  1139.870  1140.860  1139.870  1140.860       
1       2005-04-12   10:31 AM  1141.219  1141.960  1141.219  1141.960       
2       2006-04-12   12:33 PM  1142.069  1142.290  1142.069  1142.120       
3       2007-04-12    3:24 PM  1142.240  1143.140  1142.240  1143.140       
4       2008-04-12    5:32 PM  1143.350  1143.589  1143.350  1143.589       

Thanks!

Answer 1

Here, In your case 'Time' is in AM/PM format which take more time to parse.

You can add format to increase speed of to_datetime() method.

data0=pd.read_csv('filename.csv')

# %Y - year including the century
# %m - month (01 to 12)
# %d - day of the month (01 to 31)
data0['Date']=pd.to_datetime(data0['Date'], format="%Y/%m/%d")

# %I - hour, using a -hour clock (01 to 12)
# %M - minute
# %p - either am or pm according to the given time value
# data0['Time']=pd.to_datetime(data0['Time'], format="%I:%M %p") -> around 1 sec
data0['Time']=pd.datetools.to_time(data0['Time'], format="%I:%M %p")

For more methods info : Pandas Tools

For more format options check - datetime format directives.

For 500K rows it improved speed from around 60 seconds -> 0.01 seconds in my system.

You can also use :

# Combine date & time directly from string format
pd.Timestamp(data0['Date'][0] + " " + data0['Time'][0])