help sqset(SJ6-4: st0111)

Title

sqset -- Declare a dataset to be sequence data

Syntax

Declare data to be sequence data and specify element variable,
the sequence identifier and sequence order (positions)

sqset elementvar idvar ordervar
[, trim rtrim ltrim keeplongest ]

where elementvar is the variable that contains the
elements of sequences, idvar is a variable that
identifies the sequences, and ordervar is a variable that
defines the order of the sequences.

Display how dataset is currently sqset

sqset

Clear sequence data settings

sqset, clear

Description

sqset declares the data to be sequence data and designates that
elementvar represents the variable that represents the elements
of the sequences, idvar should be an identifier of the
sequences, and ordervar should be a variable that defines the
order of each sequence.

When using sqset various checks on the data are
performed, and reported back to the user.

sqset without arguments displays whether and how the
dataset is currently set.

sqset, clear is a rarely used to erase the settings from the data.

To use sqset, sequence data has to be in long format. Use
reshape to change sequence data in wide format to sequence data
in long format.

Options

trim means both, ltrim and rtrim. Generally,
we recommend using this option.

rtrim erases empty elements at the end of the
sequences. Sequence data that stem from data in wide format often
contain missing values at the end of sequences. Generally, there is no
need for these observations, so that they can simply be erased without
loss of information.

ltrim strips all empty elements at the beginning of the
sequences. Generally, all sequences should start with the element at
the first position. In practice, sequence data sometimes have one or
more empty elements at the beginning, which we call "gaps at the
beginning". Gaps at the beginning are very common for sequence data
that has its origins in unbalanced cross-sectional time-series data
(see xt). The SQ-Ados slightly differ in how they deal
with gaps at the beginning. Gaps at the beginning are, however,
somewhat ill-treated, as this means that a sequence does not start at
the first position. ltrim changes the sequence data in such a
way that all sequences starts at position one. The dataset is changed
by the option ltrim.

keeplongest keeps only the longest section of a sequence
with unknown elements at specific positions. Generally, a missing
value at a certain position in a sequence is just another element, so
there is no specific technical problem. For some commands
(i.e., sqom), it is however necessary to consider how similar the
missing value is with each of the other elements of a sequence. The
answer to this cannot be given by the SQ-Ados themselves. In order to
point the user to such problems, sqset checks for missing
elements and provides a note. The note points the user to the option
keeplongest. sqset with keeplongest will force Stata
to keep only the longest available section of a sequence that contains
missings. If several sections of a sequence have the same, Stata will
randomly select one of them. The dataset is changed by the option
keeplongest, and that keeplongest is only one of several
ways to deal with missing elements in a sequence
(see sq).

Examples

. use http://www.wz-berlin.de/~kohler/ado/youthemp, clear

. reshape long st, i(id) j(order)

. sqset st id order

Author

Ulrich Kohler, University of Potsdam, ulrich.kohler@uni-potsdam.de

Also see

Online: sq, sqdemo, sqset,
sqdes, sqegen, sqstat,
sqindexplot, sqparcoord, sqom,
sqclusterdat, sqclustermat