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psimeson

02:15

@Guesswhoitis. could you please help me understand: pd[pts_?MatrixQ, n_Integer] := (Dot @@ #[[{1, -1}]]) & /@ Partition[pts, n, n - 1] ?

Guess who it is.

02:55

@psimeson, execute test = Table[{Subscript[x, k], Subscript[y, k]}, {k, 10}].

psimeson

did it

I got a list with {{x1,y1},......,{x10,y10}}

I am having hard time understanding the part with pure function

The Toad

@psimeson You can try breaking it into smaller parts and trying with the right arguments to see what happens

#[[{1, -1}]] &@{{1, 2}, {3, 4}, {5, 6}}

Dot @@ {{1, 2}, {5, 6}}

psimeson

@TheToad Thanks.. I will try it that way.. I was trying to do so but I messed up

2012rcampion

Okay guys, I have a stupid question: If I buy 10.1, will I be able to upgrade to 10.2 through 10.xx for free?

I'm trying to decide whether I should renew my school license ($35) for another year. Currently they're only providing 10.0.1, but I do get 8 subkernels instead of 4 under the regular home-use version.

The Toad

03:11

@2012rcampion I think WRI charges for every update.

psimeson

03:25

I still don't understand what's the use of pure function pd[pts_?MatrixQ, n_Integer] := (Dot @@ #[[{1, -1}]]) & /@ Partition[pts, n, n - 1]

I can get the same result by doing this : pd[pts_?MatrixQ, n_Integer] := Dot @@@ Partition[pts, n, n - 1]

The Toad

03:56

@psimeson Are you sure about that? Have you tried comparing the two using the definition of test from above?

They don't do the same thing.

psimeson

test = {{1, 2}, {2, 3}, {4, 5}, {6, 7}, {1, 3}}

(Dot @@ #[[{1, -1}]]) & /@ Partition[test, 2, 1]

gives: {8, 23, 59, 27}

Dot @@@ Partition[test, 2, 1]

gives: {8, 23, 59, 27}

The Toad

What if you do Partition[test, 3, 2]?

psimeson

in that case i get a different result

what does this mean #[[{1, -1}]] ?

psimeson

05:04

finally understood what #[[{1, -1}]] means and how it's working :)

Guess who it is.

05:40

Oops, sorry about getting cut; I had to attend to something. I'm glad Mr. Toad was able to fill in. :)

3 hours later…

Shutao Tang

08:40

Select[
Names["System`*"],
MemberQ[Options[ToExpression@#][[All, 1]], Assumptions] &]

I'd like to know what functions contain the option of "Assumption"?

The code gives the warning information Options::opmix: Cannot mix streams and non-streams in {Courier,10.}. >> ToExpression::notstrbox: FEPrivate`FrontEndResourceString[GetFEKernelInit] is not a string or a box. ToExpression can only interpret strings or boxes as Mathematica input. >>

@2012rcampion, Could you help me to detect the problem? thks:-)

2 hours later…

halirutan

10:39

@ShutaoTang What about

names = Names["System`*"];
Quiet@Select[names,
  MemberQ[
    Function[sym, Options[Unevaluated[sym]], {HoldFirst}] @@
     MakeExpression[#], Assumptions, 2] &]

Meta

Q: Our language when we talk about Mathematica functions

The discussion in the comments in two recent AspectRatio threads (1,2) has highlighted one important aspect of our established way of expressing our thoughts about the Mathematica (or Wolfram Language) functions: we tend to use the names of built-in system Symbols instead of the corresponding wor...

discussion

1 hour later…

Szabolcs

11:56

Is there any convenient way to Merge using different functions based on keys? This is in the context of Dataset and GroupBy.

Here's an example:

data = Table[<|"name" -> #, "a" -> RandomReal[],
        "b" -> RandomReal[]|>, {RandomInteger[{3, 8}]}] & /@ {"p",
      "q", "r", "s", "t"} // Catenate // Dataset;

Now I can do data[GroupBy["name"], Merge[Total], {"a"}] or data[GroupBy["name"], Merge[Mean], {"b"}]

But I'd like to get a single dataset containing both the reduced "a" and "b" columns.

What's the simplest/shortest/easiest way?

1 hour later…

Szabolcs