closest previous year
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From: joseph Frank on 1 May 2010 07:59 Hi , I have a list of years example; A=[1990;1992;1996;1997;1998]; and I have B=1993; The year of B is not in A but I would like to find the closest previous year to this number (i.e 1992 second observation in A). Is their a function to do this ? Thanks
From: John D'Errico on 1 May 2010 08:09 "joseph Frank" <josephfrank1969(a)hotmail.com> wrote in message <hrh52c$bf6$1(a)fred.mathworks.com>... > Hi , > > I have a list of years example; > > A=[1990;1992;1996;1997;1998]; > and I have B=1993; > > The year of B is not in A but I would like to find the closest previous year to this number (i.e 1992 second observation in A). Is their a function to do this ? > Thanks Look at the second return argument from histc. John
From: dpb on 1 May 2010 08:42 joseph Frank wrote: > Hi , > > I have a list of years example; > > A=[1990;1992;1996;1997;1998]; > and I have B=1993; > > The year of B is not in A but I would like to find the closest previous > year to this number (i.e 1992 second observation in A). Is their a > function to do this ? > Thanks I didn't see the trick to John's histc() answer--I'm sure there's something obvious I'm overlooking. interpt1() has "nearest" option but won't guarantee nearest is lower than interpolant... My contribution... >> tmp=A(A<B); lowinterpolant = tmp(end) lowinterpolant = 1992 >> --
From: dpb on 1 May 2010 09:14 dpb wrote: .... > >> tmp=A(A<B); lowinterpolant = tmp(end) > lowinterpolant = > 1992 > >> Better...eliminates temporary max(A(A<B)) --
From: John D'Errico on 1 May 2010 09:54
dpb <none(a)non.net> wrote in message <hrh7nr$mj5$1(a)news.eternal-september.org>... > joseph Frank wrote: > > Hi , > > > > I have a list of years example; > > > > A=[1990;1992;1996;1997;1998]; > > and I have B=1993; > > > > The year of B is not in A but I would like to find the closest previous > > year to this number (i.e 1992 second observation in A). Is their a > > function to do this ? > > Thanks > > I didn't see the trick to John's histc() answer--I'm sure there's > something obvious I'm overlooking. Look at the help for histc. A = [1990;1992;1996;1997;1998]; [junk,index] = histc(1993,A); A(index) ans = 1992 The virtue of histc here is it is VECTORIZED and comparatively FAST as blazes. If you have a million points, still fast. The test as you have done it is not so fast. In fact, the test as you have done it is not even vectorized, so you would need to loop over multiple points. John |