How to find out Turning Points?

  • Thread starter Thread starter Guest
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Guest

How could we find out the "turning points" in a series of numbers with sorted
date? There are maybe many turning points and I don't want to see the chart
to find out those points but from those numbers. Anyone know how to do that?
 
I am not sure what you are trying to achieve by looking for "turnin
points" in sorted data.
I associate turning points with cusums (cumulative sums) where a chang
in the direction of the trend indicates a shift in the results. In thi
case finding a turning point is straightforward using a helper colum
that looks for max and min values relative to adjacent data.
Maybe if you post some data it will make it clearer
 
Thanks for your reply of my question. But it seems not solve my problem.
Say, I have a series of data like (11, 12,13,12,11,10, 9, 10, 11, 12, 11,
10, 9, 8, 9, 10), and the order of this series of numbers cannot be changed.
We could know the turning points of this series are 13, 9, 12, 8. Now, I want
to use Excel to pick up these turning points automatically. I cannot figure
out how to do this by Excel. Do you have any good idea? Thanks for your great
help agian!!

"Alex Delamain" 來函：
 
If your data is in column A starting at A2, then try the followin
starting in B3 (it wont work properly on the first or last data poin
as you don't know what the preivous/next result is)

=IF(A3=MAX(A2:A4),1,IF(A3=MIN(A2:A4),-1,""))

you can then use the autofilter to pick out the the 1's (maxima) an
-1's (minima)

Hope this help
 
And if your data is

11,12,13,13,13,12,11,10,9,10,11,12,11,10,9,8,9,10

where is the first inflection point?
 
Hi!

Might be worth looking at 1st order differences.

Your data is in A1:A18 (using Myrna's numbers).
In B2 put =A2-A1 and copy down.
The maxima and minima of the "graph" will coincide (but see later) wit
the changes of direction of the "graph". So if we can see where th
differences in column B change from + to 0 or to -, we can spot th
flexions. Do this in col C with
=IF(B2<>B3,"#","") in C3, copied down.

The # signs will show the change points.

Myrna makesa valid point that a max or min can also be a point o
inflexion (in other words a "flat spot") on the "graph, where more tha
one copy of the value happens. How flat it is will be a function of th
data and all you can do there is know where it is happening and make
rule as to how to deal with it. The # will show you where it i
happening.

If you find you need greater sophistication to handle multiple value
at maxima and minima, then you could put in further helper column
which spotted when 2 consecutive values were the same and so on
[=if(and(A1=A2 ,A2=A3)) sort of formulae].

Al
 
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