Undocumented behavior when drawing trees?

[tobi_s]

I’m using root 5.17/02 and I"m drawing some data from a tree (named ‘data’) and I was surprised by the difference in behavior between the following two:
data.Draw(“photon.E”)
data.Draw(“photon.E”, “photon.E”)

I expected the second command to be equivalent to
data.Draw(“photon.E”, TCut(“photon.E != 0”))

But this is not the case, see the attachments. The second command appears to weigh every bin with the value of photon.E in that bin. I couldn’t deduce this behavior from the documentation which is why I’m posting in this forum. Is this documented / expected behavior?

[couet]

I think it is explained here: root.cern.ch/root/html/TTree.html#TTree:Draw

[…]
selection is an expression with a combination of the columns.
In a selection all the C++ operators are authorized.

The value corresponding to the selection expression is used as a weight
to fill the histogram.

If the expression includes only boolean operations, the result
is 0 or 1. If the result is 0, the histogram is not filled.
In general, the expression may be of the form:
value*(boolean expression)
if boolean expression is true, the histogram is filled with […]

[brun]

NO!!

data.Draw("photon.E", "photon.E != 0")
is not the same as

data.Draw("photon.E","photon.E ")
With the first expression the weight of each entry is either 0 or 1 and only non-zero weights
are histogrammed.
With the second expression all entries are histogrammed with a weight equal to photon.E

Rene

[tobi_s]

Oops, I remember making the same mistake before. (!= 0) <=> true is too deeply ingrained in my brain.

Thanks!