Skip to main content

Possible bug involving Dataset/Query and RightComposition


Bug introduced in 10.0.0 and fixed in 10.0.1



Short Version


Why are the results of the following expressions different?


Dataset[{1, 2}][f /* g, z]
Dataset[<|x->1, y->2|>][Values /* f /* g, z]

(*
g[f[{z[1],z[2]}]]

g[f[z[{1,2}]]]
*)

Long Version


Consider the following dataset queries:


Dataset[{1, 2}][f , z]
Dataset[{1, 2}][f /* g, z]
Dataset[{1, 2}][f /* g /* h, z]

(*

f[{z[1],z[2]}]
g[f[{z[1],z[2]}]]
h[g[f[{z[1],z[2]}]]]
*)

The results are as expected, with the ascending operators f, z, etc. being applied from the lowest level outward. But now consider these queries:


Dataset[<|x->1, y->2|>][Values /* f, z]
Dataset[<|x->1, y->2|>][Values /* f /* g, z]
Dataset[<|x->1, y->2|>][Values /* f /* g /*h, z]


(*
f[{z[1],z[2]}]
g[f[z[{1,2}]]]
h[g[z[f[{1,2}]]]]
*)

This time, Values is used to ignore the keys in the assocation. The level 1 query operator is a composition of a descending operator with one or more ascending operators. The documentation has this to say:



When one or more descending operators are composed with one or more ascending operators (e.g. desc /* asc), the descending part will be applied, then subsequent operators will be applied to deeper levels, and lastly the ascending part will be applied to the result.




Yet note how in the second query the level two ascending operator z is no longer applied to the level two elements. Worse still, in the third query the level 2 ascending operator z is being applied after the level 1 ascending operator f.


The operator reordering is most apparent in the "compiled" forms of the queries:


Dataset`CompileQuery[Values /* f, z]
Dataset`CompileQuery[Values /* f /* g, z]
Dataset`CompileQuery[Values /* f /* g /*h, z]

(*
Dataset`WithOverrides@*GeneralUtilities`Checked[Values/*Map[z]/*f,Identity]
Dataset`WithOverrides@*GeneralUtilities`Checked[Values/*f/*Map[z]/*g,Identity]
Dataset`WithOverrides@*GeneralUtilities`Checked[Values/*f/*g/*Map[z]/*h,Identity]

*)

Is this a bug, or a gap in my understanding?


Update


In a comment below, @TaliesinBeynon confirms that this is a bug that will be fixed in v10.0.1.



Answer



Workaround


Even though I cannot explain the behaviour, I note that the level one ascending operators will remain right-composed by means of a level one subquery or by a subsequent query:


Dataset[<|x->1, y->2|>][Values /* Query[f /* g /*h], z]
Dataset[<|x->1, y->2|>][Values, z][f /* g /*h]


(*
h[g[f[{z[1],z[2]}]]]
h[g[f[{z[1],z[2]}]]]
*)

Comments

Post a Comment

Popular posts from this blog

plotting - How to draw lines between specified dots on ListPlot?

I would like to create a plot where I have unconnected dots and some connected. So far, I have figured out how to draw the dots. My code is the following: ListPlot[{{1, 1}, {2, 2}, {3, 3}, {4, 4}, {1, 4}, {2, 5}, {3, 6}, {4, 7}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {1, 10}, {2, 11}, {3, 12}, {4,13}, {2.5, 7}}, Ticks -> {{1, 2, 3, 4}, None}, AxesStyle -> Thin, TicksStyle -> Directive[Black, Bold, 12], Mesh -> Full] I have thought using ListLinePlot command, but I don't know how to specify to the command to draw only selected lines between the dots. Do have any suggestions/hints on how to do that? Thank you. Answer One possibility would be to use Epilog with Line : ListPlot[ {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {1, 4}, {2, 5}, {3, 6}, {4, 7}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {1, 10}, {2, 11}, {3, 12}, {4, 13}, {2.5, 7}}, Ticks -> {{1, 2, 3, 4}, None}, AxesStyle -> Thin, TicksStyle -> Directive[Black, Bold, 12], Mesh -> Full, Epilog -> { Line[ ...
Post a Comment
Read more

equation solving - Invert and fit implicitly defined curve

I need to fit an implicitly defined curve. I thought I could get some data out of Solve , and then using FindFit . Therefore, I would like to find the relation the parametric curve defined by $F(x,y)=0$: Solve[-(1/2) + 1/2 (0.41202 BesselK[0, 0.1 Sqrt[x^2 + y^2]] + (0.101483 x BesselK[1, 0.1 Sqrt[x^2 + y^2]])/Sqrt[x^2 + y^2]) == 0, y] But I can't get an output: Solve was unable to solve the system with inexact coefficients or the system obtained by direct rationalization of inexact numbers present in the system. Since many of the methods used by Solve require exact input, providing Solve with an exact version of the system may help. >> Edit: In particular, I would like to fit the data coming from the curve with the expression of another curve, and not with a function $f(x)$. In particular, since this clearly looks like a cardioid , I would like it to fit to something like it. What other strategies could I try?
Post a Comment
Read more

dynamic - How can I make a clickable ArrayPlot that returns input?

I would like to create a dynamic ArrayPlot so that the rectangles, when clicked, provide the input. Can I use ArrayPlot for this? Or is there something else I should have to use? Answer ArrayPlot is much more than just a simple array like Grid : it represents a ranged 2D dataset, and its visualization can be finetuned by options like DataReversed and DataRange . These features make it quite complicated to reproduce the same layout and order with Grid . Here I offer AnnotatedArrayPlot which comes in handy when your dataset is more than just a flat 2D array. The dynamic interface allows highlighting individual cells and possibly interacting with them. AnnotatedArrayPlot works the same way as ArrayPlot and accepts the same options plus Enabled , HighlightCoordinates , HighlightStyle and HighlightElementFunction . data = {{Missing["HasSomeMoreData"], GrayLevel[ 1], {RGBColor[0, 1, 1], RGBColor[0, 0, 1], GrayLevel[1]}, RGBColor[0, 1, 0]}, {GrayLevel[0], GrayLevel...
Post a Comment
Read more