Re: sparsearray and its nonempty cells
- To: mathgroup at smc.vnet.net
- Subject: [mg72648] Re: sparsearray and its nonempty cells
- From: Arkadiusz.Majka at gmail.com
- Date: Sat, 13 Jan 2007 05:02:13 -0500 (EST)
- References: <eo4oa3$mhi$1@smc.vnet.net><eo7njr$20l$1@smc.vnet.net>
DearAll, Of course I can simply use Sort but I would prefer to obtain already sorted list directly from Mysparse/. SparseArray[_, _, _, x_] :> x[[2, 2]] or from ArrayRules[...]. BTW Most[First/@ArrayRules[Mysparse]] does not produce sorted list despite what dh wrote. In practice I have very long list Mysparse/. SparseArray[_, _, _, x_] :> x[[2, 2]] and I want to take the maximum of it. This searching takes some time. If I would have sorted list (given in advance) I would take the last element. Take again: Out[279]= SparseArray[i_ /; 2 â?¤ i â?¤ 4 :> A, 6] In[280]:= % /. SparseArray[_, _, _, x_] :> x[[2,2]] {{3}, {2}, {4}} and: SparseArray[i_ /; 2 â?¤ i â?¤ 4 :> A, 6]//Trace {{i_ /; 2 â?¤ i â?¤ 4 :> A, i_ /; 2 â?¤ i â?¤ 4 :> A}, SparseArray[i_ /; 2 â?¤ i â?¤ 4 :> A, 6], {2 â?¤ 1 â?¤ 4, False}, {2 â?¤ 2 â?¤ 4, True}, {2 â?¤ 3 â?¤ 4, True}, {2 â?¤ 4 â?¤ 4, True}, {2 â?¤ 5 â?¤ 4, False}, {2 â?¤ 6 â?¤ 4, False}, SparseArray[<\[InvisibleSpace]3\[InvisibleSpace]>, {6}]} Note, that True is for 2, 3 and 4 - ordered! Wht do you think? Arek dh napisaÅ?(a): > Hi Arek, > if you say: Mysparse // FullForm you will see that the array is not > stored in ascending order as you imply. To get your output sorted, > simply wrap Sort around it. > Daniel > > Arkadiusz.Majka at gmail.com wrote: > > Hi, > > > > I bulit the following sparse array > > > > Mysparse=SparseArray[i_ /; 2 â?¤ i â?¤ 11 :> 0.8, 20] > > > > in order to find out all nonempty cells in this array I call (I want to > > avoid Normal) > > > > > > Mysparse/. SparseArray[_, _, _, x_] :> x[[2, 2]] > > > > and I get > > > > {{8}, {11}, {3}, {7}, {2}, {6}, {10}, {9}, {5}, {4}} > > > > This is of course correct, but why it is not sorted???? > > > > How can I build Mysparse to get sorted list of nonempty cells? > > > > Arek > >
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