User`s guide

1 Data Processing
Selecting Subsets of Data
In this section...
“Why Select Subse ts of Data?” on page 1-86
“Selecting Data Using the GUI” on page 1-87
“Selecting Data at the Com mand L ine” on page 1-89
Why Select S ubsets of Data?
You can use data selection to cre ate independent data sets for estimation
and validation.
You can also use data selection as a way to clean the data and exclude parts
with noisy or missing information. For example, when your d ata contains
missing values, outliers, level changes, and disturbances, you can select one
or more portions of the data that are suitable for identification and exclude
the rest.
If you only have one data set and you w ant to estimate linear models, you
should split the data into two portions to create tw o independent data s ets for
estimation and validation, respectively. Splitting the data is selecting parts of
the data set and saving each part independently.
You can m e r ge s everal data segments into a single multi experiment d ata s e t
and identify an average model. For more information, see “Representing Data
in the GUI” on page 1-13 o r “Representing Time- and Frequency-Do main Data
Using iddata Objects” on page 1-47.
Note Subsets of the data set must contain e nough samples to adequately
represent the system, and the inputs must provide suitable excitation to the
system.
Selecting potions of frequency-domain data is equivalent to filtering the data.
For more information about filterin g, see “Filter in g Da t a” on page 1-10 7.
1-86