I/O shell formatting

[genedan]

While working on #856, I came across numeric formatting options that we currently don't offer in cl.Options. These would be things like display precision and thousands separators. I also noticed the potential for adding formatting options when reviewing @henrydingliu's work on the Friedland reconciliation and summary exhibits.

There is some amount of custom formatting done internally, such as adding a thousands separator and changing the precision based on the magnitude of the triangle's values when displaying in a Jupyter Notebook:

chainladder-python/chainladder/core/display.py

Lines 99 to 117 in 449b5c1

	@staticmethod
	def _get_format_str(data: DataFrame) -> str:
	"""
	Returns a numerical format string based on the magnitude of the mean absolute value of the values in the
	supplied DataFrame.
	Returns
	-------
	str
	"""
	if np.all(np.isnan(data)):
	return ""
	elif np.nanmean(abs(data)) < 10:
	return "{0:,.4f}"
	elif np.nanmean(abs(data)) < 1000:
	return "{0:,.2f}"
	else:
	return "{:,.0f}"

This can be seen on the onboarding tutorials in the differences between the display of a Pandas DataFrame and Chainladder Triangle:

I think for printing to console, chainladder defaults to whatever the pandas settings are:

raa = cl.load_sample('raa')
raa
Out[4]: 
         12       24       36       48       60       72       84       96       108      120
1981  5012.0   8269.0  10907.0  11805.0  13539.0  16181.0  18009.0  18608.0  18662.0  18834.0
1982   106.0   4285.0   5396.0  10666.0  13782.0  15599.0  15496.0  16169.0  16704.0      NaN
1983  3410.0   8992.0  13873.0  16141.0  18735.0  22214.0  22863.0  23466.0      NaN      NaN
1984  5655.0  11555.0  15766.0  21266.0  23425.0  26083.0  27067.0      NaN      NaN      NaN
1985  1092.0   9565.0  15836.0  22169.0  25955.0  26180.0      NaN      NaN      NaN      NaN
1986  1513.0   6445.0  11702.0  12935.0  15852.0      NaN      NaN      NaN      NaN      NaN
1987   557.0   4020.0  10946.0  12314.0      NaN      NaN      NaN      NaN      NaN      NaN
1988  1351.0   6947.0  13112.0      NaN      NaN      NaN      NaN      NaN      NaN      NaN
1989  3133.0   5395.0      NaN      NaN      NaN      NaN      NaN      NaN      NaN      NaN
1990  2063.0      NaN      NaN      NaN      NaN      NaN      NaN      NaN      NaN      NaN
raa.link_ratio
Out[5]: 
          12-24     24-36     36-48     48-60     60-72     72-84     84-96    96-108   108-120
1981   1.649840  1.319023  1.082332  1.146887  1.195140  1.112972  1.033261  1.002902  1.009217
1982  40.424528  1.259277  1.976649  1.292143  1.131839  0.993397  1.043431  1.033088       NaN
1983   2.636950  1.542816  1.163483  1.160709  1.185695  1.029216  1.026374       NaN       NaN
1984   2.043324  1.364431  1.348852  1.101524  1.113469  1.037726       NaN       NaN       NaN
1985   8.759158  1.655619  1.399912  1.170779  1.008669       NaN       NaN       NaN       NaN
1986   4.259749  1.815671  1.105367  1.225512       NaN       NaN       NaN       NaN       NaN
1987   7.217235  2.722886  1.124977       NaN       NaN       NaN       NaN       NaN       NaN
1988   5.142117  1.887433       NaN       NaN       NaN       NaN       NaN       NaN       NaN
1989   1.721992       NaN       NaN       NaN       NaN       NaN       NaN       NaN       NaN

Unless there's another way, I think when printing to console, you'd need to adjust the Pandas settings. You'd need to do this for individual triangles, as changing session-wide settings makes no distinction between loss and link ratio values:

import pandas as pd
pd.options.display.float_format = "{:,.0f}".format
raa
Out[10]: 
       12     24     36     48     60     72     84     96     108    120
1981 5,012  8,269 10,907 11,805 13,539 16,181 18,009 18,608 18,662 18,834
1982   106  4,285  5,396 10,666 13,782 15,599 15,496 16,169 16,704    NaN
1983 3,410  8,992 13,873 16,141 18,735 22,214 22,863 23,466    NaN    NaN
1984 5,655 11,555 15,766 21,266 23,425 26,083 27,067    NaN    NaN    NaN
1985 1,092  9,565 15,836 22,169 25,955 26,180    NaN    NaN    NaN    NaN
1986 1,513  6,445 11,702 12,935 15,852    NaN    NaN    NaN    NaN    NaN
1987   557  4,020 10,946 12,314    NaN    NaN    NaN    NaN    NaN    NaN
1988 1,351  6,947 13,112    NaN    NaN    NaN    NaN    NaN    NaN    NaN
1989 3,133  5,395    NaN    NaN    NaN    NaN    NaN    NaN    NaN    NaN
1990 2,063    NaN    NaN    NaN    NaN    NaN    NaN    NaN    NaN    NaN
raa.link_ratio
Out[11]: 
      12-24  24-36  36-48  48-60  60-72  72-84  84-96  96-108  108-120
1981      2      1      1      1      1      1      1       1        1
1982     40      1      2      1      1      1      1       1      NaN
1983      3      2      1      1      1      1      1     NaN      NaN
1984      2      1      1      1      1      1    NaN     NaN      NaN
1985      9      2      1      1      1    NaN    NaN     NaN      NaN
1986      4      2      1      1    NaN    NaN    NaN     NaN      NaN
1987      7      3      1    NaN    NaN    NaN    NaN     NaN      NaN
1988      5      2    NaN    NaN    NaN    NaN    NaN     NaN      NaN
1989      2    NaN    NaN    NaN    NaN    NaN    NaN     NaN      NaN

I'm mostly jotting down these thoughts so I don't forget, and I currently don't have a request specific enough to turn into an issue. I also wanted to start a discussion gauge how useful having chainladder-level options to control the formatting would be. I think at a minimum though, we should move any default formatting to a central location in the library, such as __init__.py where all the current options are, which we could expand to its own module if it gets big enough.

[henrydingliu]

being able to easy set the display to be in thousands or millions would be great. I rely on displaying triangles in notebooks quite a bit.