diff general/funutils/groupby.m @ 4:e44f49929e56

Adding reorganised general toolbox, now in several subdirectories.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/general/funutils/groupby.m	Sat Jan 12 19:21:22 2013 +0000
@@ -0,0 +1,21 @@
+function y=groupby_or(f,x)
+% groupby_or - collect rows of x into equivalence classes based f
+%
+% groupby_or :: ([[1,M]]->A), [[N,M]] -> {[K]->[[L,M]]} :- equality(A).
+%
+% IMPORTANT: this version assumes that data is ordered by f, that is,
+% only consecutive rows will be grouped together.
+
+	N=size(x,1);
+	y={}; 
+	
+	i=1; j=1;
+	while j<=N
+		if i==j, z=f(x(i,:)); end
+		if j==N || f(x(j+1,:)~=z)
+			y=vertcat(y,{x(i:j,:)});
+			i=j+1; j=i;
+		else j=j+1; 
+		end
+	end
+