@backtrader Please look at the above illustration. Thanks in advance.

Yes, I have a custom filter, I'm trying to aggregate data in price bars. In the small illustration below, I'm trying to make a new line 'priceDiff'. The line 'Ltp' is already defined in a custom feed deriving GenericCSVData class.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Wed Dec 11 06:41:45 2019

@author: akul
"""
#!/usr/bin/env python
# -*- coding: utf-8; py-indent-offset:4 -*-
###############################################################################
#
# Copyright (C) 2015, 2016, 2017 Daniel Rodriguez
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
###############################################################################
from __future__ import (absolute_import, division, print_function,
                        unicode_literals)


from . import Filter


__all__ = ['RangeBarFilter']


class RangeBarFilter(Filter):
    '''Modify the data stream to create rangebars of price change similar to Renko

    Params:

      - ``size`` (default: *None*) The size to consider for each brick

      - ``autosize`` (default: *20.0*) If *size* is *None*, this will be used
        to autocalculate the size of the bricks (simply dividing the current
        price by the given value)

      - ``align`` (default: *1.0*) Factor use to align the price boundaries of
        the bricks. If the price is for example *3563.25* and *align* is
        *10.0*, the resulting aligned price will be *3560*. The calculation:

          - 3563.25 / 10.0 = 356.325
          - round it and remove the decimals -> 356
          - 356 * 10.0 -> 3560

    See:
      - http://stockcharts.com/school/doku.php?id=chart_school:chart_analysis:renko

    '''

    params = (
        ('size', None),
        ('autosize', 250.0),
        ('align', 1.0),
    )

    def nextstart(self, data):
        o = data.lines.Ltp[0]
        o = round(o / self.p.align, 0) * self.p.align  # aligned
        self._size = self.p.size or float(o // self.p.autosize)
        self._top = int(o) + self._size
        self._bot = int(o) - self._size
        self.initialPrice = data.lines.Ltp[0]
        
    def next(self, data):
        
        if (data.lines.Ltp[0] > self._top) or (data.lines.Ltp[0] < self._bot):
            data.lines.priceDiff[0] = data.lines.Ltp[0] - self.initialPrice
            self.initialPrice = None
            o = data.lines.Ltp[0]
            o = round(o / self.p.align, 0) * self.p.align  # aligned
            self._size = self.p.size or float(o // self.p.autosize)
            self._top = int(o) + self._size
            self._bot = int(o) - self._size
            return False  # length of data stream is unaltered

        if(not self.initialPrice):
           self.initialPrice  = data.lines.Ltp[0]
        data.backwards()
        return True  # length of stream was changed, get new bar
 

The error I get it something like this,

Traceback (most recent call last):
  File "testpandas.py", line 52, in <module>
    cerebro.run()
  File "/home/akul/Documents/backtrader/cerebro.py", line 1127, in run
    runstrat = self.runstrategies(iterstrat)
  File "/home/akul/Documents/backtrader/cerebro.py", line 1212, in runstrategies
    data.preload()
  File "/home/akul/Documents/backtrader/feed.py", line 688, in preload
    while self.load():
  File "/home/akul/Documents/backtrader/feed.py", line 523, in load
    retff = ff(self, *fargs, **fkwargs)
  File "/home/akul/Documents/backtrader/flt.py", line 48, in __call__
    self.next(data)
  File "/home/akul/Documents/backtrader/filters/rangeBarFilter.py", line 94, in next
    data.lines.priceDiff[0] = data.lines.Ltp[0] - self.initialPrice
AttributeError: 'Lines_LineSeries_DataSeries_OHLC_OHLCDateTime_Abst' object has no attribute 'priceDiff'

Hi all,
I downsampled data feed using filters to make price bars. Now there is some information that I want to retain with the new data feed for eg, total qty traded within the price bar, which I did on by updating a column names Qty.

But let's say I want to retain additional information eg timeDelta, priceDelta, etc., I would require additional columns in the data itself.

How to add such columns while applying a filter to a data feed?

@backtrader said in Cumulative/Running mean implementation:

Thanks, anyways I created my own indicator. Btw I meant Expanding mean ie. avg[i] = avg(df[0:i]).

I have just started with backtrader. I am looking to add cumulative mean as an indicator. I could not find anything like this in the default indicators. Can someone guide me if anyone has already coded it?