TTree CSV export

[cdeil]

It would be nice if it were easily possible to display or export TTree data (if possible after column and row selection) as CSV (comma-separated values).

[pwaller]

How should we implement this? We could make a recarray and then convert it to a CSV, but that would we wasteful. However, it would be easy, and might be a good starting point. I'm not sure we want to(/can) support huge trees initially anyway.

Given a method of turning a TTree into a CSV this is pretty trivial to implement. Just look at scan.

[cdeil]

I think TTree -> recarray -> CSV is fine for now ... for gigabytes you don't want CSV anyways.

Thanks for the link to scan, I'll give it a try tomorrow.

[pwaller]

Sounds good to me, let me know how it goes :)

[cdeil]

The WebOOT part was trivial ... now how do I generate the CSV?

I wanted to convert to a rootpy.tree.Tree and then call the csv method on it into a in-memory StringIO.

• Am I allowed to use rootpy in weboot?
• Is it possible to do the TTree -> Tree conversion in-memory or do I have to create a temp file?

[pwaller]

Yes, you can use rootpy in weboot.

TTree -> Tree should be easy through tree = rootpy.asrootpy(ttree), so far as I know. @ndawe, comments?

[cdeil]

I'll wait until rootpy/rootpy#251 is resolved before finishing this.

[cdeil]

Still doesn't work. I get this in the browser when hitting toy_sigbkg.root/TreeB/!csv/a:

['var1', 'var2', 'var3', 'var4', 'weight']

[ (-2.7639870643615723, -1.4941457509994507, -1.616673231124878, -2.917888641357422, 0.10676071792840958)
 (-0.7001328468322754, -1.344607949256897, -0.8229119777679443, -1.3939814567565918, 0.892978310585022)
 (3.4071643352508545, 1.9969775676727295, 2.607431650161743, 3.4646029472351074, 0.001675486913882196)]

data = stream.read() is empty.

What am I doing wrong?

[cdeil]

@pwaller I'd like to get this done. Can you try the URL toy_sigbkg.root/TreeB/!csv/a with this branch to see if the issue is at least reproducible?

[pwaller]

@cdeil, okay, if you want to get a StringIO()'s contents, the function you want is stringio.getvalue(). That will give you the full contents of the buffer.

The reason .read() doesn't work is that .read() gets content from "the current file offset`. The current file offset moves with rights, therefore, it's right at the end of the buffer, where you read nothing.

HTH. Do you follow?

[cdeil]

Ah ... stupid mistake ... thanks for checking!

The URL toy_sigbkg.root/TreeB/!csv now gives

var1,var2,var3,var4,weight
-2.76398706436,-1.494145751,-1.61667323112,-2.91788864136,0.106760717928
-0.700132846832,-1.34460794926,-0.822911977768,-1.39398145676,0.892978310585
3.40716433525,1.99697756767,2.60743165016,3.46460294724,0.00167548691388
...

and hsimple.root/ntuple/!csv works as well.

@pwaller Ready to merge?