resample irregularly spaced data in pandas

You don't need to explicitly use DatetimeIndex, just set 'time' as the index and pandas will take care of the rest, so long as your 'time' column has been converted to datetime using pd.to_datetime or some other method. Additionally, you don't need to resample each column individually if you're using the same method; just do it on the entire DataFrame.

# Convert to datetime, if necessary.
df['time'] = pd.to_datetime(df['time'])

# Set the index and resample (using month start freq for compact output).
df = df.set_index('time')
df = df.resample('MS').mean()

The resulting output:

            fraction  number
time                        
2014-10-01  0.435441     0.5
2014-11-01  0.430544     6.5
2014-12-01  0.627552    13.5