scatstat1documentation
Thescatstat1function returns statistical values of all points within a given 1D radius of each value. This is similar to taking a moving mean, but points do not have to be equally spaced, nor do x values need to be monotonically increasing.
See alsoscatstat2.
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Contents
Syntax
ybar = scatstat1(x,y,radius) ybar = scatstat1(x,y,radius,fun) ybar = scatstat1(...,options)
Description
ybar = scatstat1(x,y,radius)returns the mean of allyvalues within specifiedradiusat each pointx.
ybar = scatstat1(x,y,radius,fun)applies any functionfuntoyvalues, defaultfunis@mean, but could be@median,@nanstd, etc.
ybar = scatstat1(...,options)allows any options that the function accepts. For example,'omitnan'.
Example 1
Get the local median of all points within 10 units of each x point. Start by creating some random non-sorted data with N = 10,000 points:
N = 10000; x = randi(300,N,1) + 20+3*randn(N,1) ; y = 3*sind(x) + randn(size(x)) + 3; plot(x,y,'k.') axistightboxoff
Now get the moving median of all points within 15 x units of each value:
yb = scatstat1(x,y,15,@median,'omitnan'); holdonplot(x,yb,'bo')
Note, this function does not interpolate or enforce any equal spacing. Final values correspond to each x point, which need not be equally spaced or sorted. Here's a zoom-in so you can see that the x values are not equally spaced:
axis([167 173 1 6])
Example 2: Sea ice data
From 1978 to 1988 the NSIDC sea ice time series contains about one measurement about every two days. After 1988, it's a daily time series. What if you want a 2 year moving average of sea ice time series, on this dataset which does not have constant temporal resolution?
Here's the situation:
loadseaice_extent.mat% loads the sample datafigure plot(t,extent_N) axistightboxoffylabel'northern hemisphere sea ice extent 1\times10^6 km)'
Before 1988, the data is available every other day, and then there's a gap in the data, and then it's daily data. Plot the time between measurements (in days) as the gradient of thedatenumvalues:
figure plot(t,gradient(datenum(t))) ntitle'days between measurements'boxoff
You see, there's a gap.
For a two-year moving average (a radius of 1 year), convert the datetime formatttodatenumformat, and usescatstat1with a radius of 365.25 days:
extent_N_2yr = scatstat1(datenum(t),extent_N,365.25); figure(1)% goes back to the sea ice time series figureholdonplot(t,extent_N_2yr,'k','linewidth',2)
当然,你可能不愿意信任一个ything within 1 radius (1 year for the 2 year moving average) of the ends, which is why the strange wiggles appear on at the start and end of the time series.
Author info:
This function was written byChad A. Greeneof the University of Texas at Austin's Institute for Geophysics (UTIG), June 2016.