downsample_ts

Calculate monthly means, annual medians, and other statistics for 1D or 3D datasets.

This function downsamples 1D or 3D data to monthly, yearly, hourly, minutely, or secondly data. This function was originally designed to create monthly mean time series from daily geospatial climate data.
Syntax
Z_downsamp = downsample_ts(Z,t)
Z_downsamp = downsample_ts(...,'DownsamplingPeriod')
Z_downsamp = downsample_ts(...,'function')
[Z_downsamp,t_downsamp] = downsample_ts(...)

Description
Z_downsamp = downsample_ts(Z,t) downsamples Z, which must be provided with a corresponding time vector t. Z can be 1D if its length matches the length of t. If Z is three-dimensional, the length of its third dimension must match the length of t. For geospatial climate data arrays, dimensions of Z might correspond to lat x lon x time or lon x lat x time.

Z_downsamp = downsample_ts(...,'DownsamplingPeriod') specifies a downsampling period as

'year'
'month' (default)
'day'
'hour'
'minute'
'second'

Z_downsamp = downsample_ts(...,'function') specifies a function to perform on the data. By default, monthly averages are taken, but you may wish to return the monthly median or monthly standard deviation or any of the functions listed below.

A note on functions which ignore NaNs: To get the monthly means of data while ignoring NaN values, you can use the 'nanmean' option. The nanmean function is part of the Statistics Toolbox, but may also be found as part of the NaN Suite on File Exchange. However, the File Exchange versions mix up the order of dimensions and flags for nanstd, nanvar, nanmin, and nanmax, so you will need the Statistics Toolbox for those particular functions. In all, the following functions are available:

'mean' (default)
'nanmean' ignores NaN values in Z. Requires Statistics toolbox or NaN Suite.
'median'
'nanmedian' ignores NaN values in Z. Requires Statistics toolbox or NaN Suite.
'min'
'nanmin' ignores NaN values in Z. Requires Statistics toolbox.
'max'
'nanmax' ignores NaN values in Z. Requires Statistics toolbox.
'std' standard deviation.
'nanstd' ignores NaN values in Z. Requires Statistics toolbox.
'var' variance.
'nanvar' ignores NaN values in Z. Requires Statistics toolbox.
'mode'
'sum'
'nansum'

[Z_downsamp,t_downsamp] = downsample_ts(...) also returns a time array corresponding to Z_downsamp. If Z is 3D or, t_downsamp corresponds to the third dimension of Z_downsamp. Each value in t_downsamp represents the mean time of all data contributing to that slice of Z_downsamp.