[DF] Beauty fixes to Display #9116
Description
Current output:
root [5] ROOT::RDataFrame(10).Define("x", "rdfentry_").Define("y", "rdfentry_*2").Display()->Print()
x | y |
0 | 0 |
1 | 2 |
2 | 4 |
3 | 6 |
4 | 8 |
Desired output is more like (suggestions welcome):
entry | x | y |
---------------
0 | 0 | 0 |
---------------
1 | 1 | 2 |
---------------
2 | 2 | 4 |
---------------
3 | 3 | 6 |
---------------
4 | 4 | 8 |
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