Re: Intersection of sublists on date and making a 2D list from a 3D one

*To*: mathgroup at smc.vnet.net*Subject*: [mg109927] Re: Intersection of sublists on date and making a 2D list from a 3D one*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sun, 23 May 2010 03:17:20 -0400 (EDT)

On 5/22/10 at 12:42 AM, warsaw95826 at mypacks.net (Garapata) wrote: >I have a list with the following dimensionality: > Dimensions[list] > Dimensions[list[[1]]] > Dimensions[list[[2]]] > Dimensions[list[[3]]] You can get exactly the same result using Map (shorthand /@) here. That is Dimensions[list[ Dimensions/@list yields the same result as you posted >I think of it as 3 groups, each with a different number of rows, but >each of these rows has 3 columns. Of the 3 columns, the third has >dates in a DateList format. >So, I can simulate the list with the following: >a = Table[{RandomInteger[10], RandomInteger[10], DatePlus[{2010, 1, >1}, RandomInteger[{1, 150}]]}, {1}, {191}]; list = Join[a[[All, 4 ;; >133, All]], a[[All, 1 ;; 126, All]], a]; >Ultimately I'd like to find all the rows that intersect on the same >dates and put the whole thing into a 2 dimensional structure that >would have the following columns: >commonDates, group1Data1, group1Data2, group2Data1, group2Data2, >group3Data1, group3Data2, >I can use Intersect[] to find the common dates: >Intersection[list[[1, All,3]], list[[2, All, 3]], list[[3, All, >3]]]; >but this seems a bit cumbersome given I may have a greater or lesser >number of groups. Seems like I need to start this in a better way, >but since Intersection[] doesn't take a list of lists I don't know >where to take this. much less cumbersome is using Map and Apply, that is commonDates=Intersection@@(#[[All,3]]&/@list); Once you have the common dates, you can select the desired data using Cases as follows Cases[SortBy[#,Last],{__,_?(MemberQ[commonDates,#]&)]]&/@list