Something wrong with the way units are handled in V10

Question

(This applies only to version 10)

I obtain these two properties of silicon:

a = ElementData[14, "CrustAbundance"]
b = ElementData[14, "MeteoriteAbundance"]

both are given in units of g/g. Then I divide these two values

a/b

and get an odd result, which with I cannot further reasonably calculate with or plot.

(Quantity[0.000034, ("Grams")/("Grams")]) Quantity[3.6*10^6, (1/#1 &)[("Grams")/("Grams")]]

Yep, you only get units in V10. I should have added this: only in V10. — Mockup Dungeon, Oct 23 '14 at 11:56
@MockupDungeon Well, just click the edit link and add it than (you can also add the correct tag). — Ajasja, Oct 23 '14 at 11:57
As a workaround, since you know that the "Grams"/"Grams" should provide a dimensionless value, use QuantityMagnitude. a = ElementData[14, "CrustAbundance"] // QuantityMagnitude; b = ElementData[14, "MeteoriteAbundance"] // QuantityMagnitude; a/b gives 1.9. — Bob Hanlon, Oct 23 '14 at 14:28
@BobHanlon OK, yes that works, but it still seems something is wrong with the data from Wolfram. — Mockup Dungeon, Oct 23 '14 at 14:44

score 4 · Answer 1 · answered Oct 23 '14 at 16:48

This is definitely bad behavior in the units code; here's the simpler version:

In[12]:= Power[Quantity[2, "Grams"/"Grams"], -1]
Out[12]= Quantity[1/2, (1/#1 &)[("Grams")/("Grams")]]

I've already sent a report to developers about this, but as an additional work-around you can use UnitSimplify on the results from ElementData to get the simpler(nondimensional) form:

In[17]:= UnitSimplify[ElementData[14, "CrustAbundance"]]
Out[17]= 0.27

and UnitSimplify won't remove quantity expressions if the units still belong:

In[19]:= UnitSimplify[ElementData[14, "VickersHardness"]]
Out[19]= Quantity[9.63*10^3, "Megapascals"]

score 4 · Answer 2 · edited Apr 13 '17 at 12:55

4

In my opinion, units provided by the curated data sets aren't quite ready prime time, and therefore I use this answer to shut them off.

SetSystemOptions[SystemOptions["DataOptions"] /. True -> False]

a = ElementData[14, "CrustAbundance"]
b = ElementData[14, "MeteoriteAbundance"]
a/b
(* 0.27, 0.14, 2 *)

edited Apr 13 '17 at 12:55

Community

1

answered Oct 23 '14 at 17:02

bobthechemist

19,693
4
52
138

Something wrong with the way units are handled in V10

2 Answers2