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factor or ordered var, even if two variables share the same level labels. Besides
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factor or ordered var, even if two variables share the same level labels. Besides
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storing the level data, it is used to mark a column as being a factor.}
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storing the level data, it is used to mark a column as being a factor.}
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}
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}
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SDF's are managed in a workspace separate from R's. When SQLiteDF is loaded, it searches
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SDF's are managed in a workspace separate from R's. When SQLiteDF is loaded, it searches
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for the file \code{workspace.db} in the current working directory. This file contains
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for the file \code{workspace.db} inside the subdirectory \code{.SQLiteDF} in the current
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working directory. This file contains
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a list of SDF's created/used in the previous session (i.e. SQLiteDF sessions are automatically
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a list of SDF's created/used in the previous session (i.e. SQLiteDF sessions are automatically
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saved), including their full and relative path and attach information.
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saved), including their full and relative path and attach information.
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Workspace is managed using the SQLite engine
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Workspace is managed using the SQLite engine
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by opening \code{workspace.db} as the main database and then attaching (SQLite's attach) the SDF's.
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by opening \code{workspace.db} as the main database and then attaching (SQLite's attach) the SDF's.
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Unfortunately, the number of attached databases is limited to 31 (actually 32, but 1 is reserved
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Unfortunately, the number of attached databases is limited to 31 (actually 32, but 1 is reserved
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for the temp db). Therefore, SDF's are \emph{scored} according to the number of times
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for the temp db). Therefore, SDF's are \emph{scored} according to the number of times
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it has been used. When the maximum allowed attachment is reached, the least used attached
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it has been used. When the maximum allowed attachment is reached, the least used attached
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SDF's is detached and the needed one is attached in its place. The packaged SQLite3 static library
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SDF's is detached and the needed one is attached in its place. On compiling the package, the
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configure script modifies the bundled SQLite source such that
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has been modified to have 31 maximum attachments, because the default is 10.
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constant controlling the maximum attachments is modified to 31 (default is 10).
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Back to when SQLiteDF is loaded, after opening \code{workspace.db}, the SDF's stored in the list
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Back to when SQLiteDF is loaded, after opening \code{workspace.db}, the SDF's stored in the list
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are sorted according to their number of uses in the previous session and then the
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are sorted according to their number of uses in the previous session and then the
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first 30 are attached. The relative path is used for finding the SDF file. If the file
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first 30 are attached. The relative path is used for finding the SQLite file. If the file
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cannot be found, it is deleted from the SQLiteDF workspace (with a warning message). The
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cannot be found, it is deleted from the SQLiteDF workspace (with a warning message). The
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scores are then all reset.
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scores are then all reset.
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A sqlite.data.frame object is a list a single element:
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A sqlite.data.frame object is a list a single element:
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\itemize{
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\itemize{
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and the following attributes:
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and the following attributes:
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\itemize{
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\itemize{
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\item{class}{The S3 class vector \code{c("sqlite.data.frame", "data.frame")}}
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\item{class}{The S3 class vector \code{c("sqlite.data.frame", "data.frame")}}
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\item{row.names}{A sqlite.vector of mode character containing the row names of the SDF}
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\item{row.names}{A sqlite.vector of mode character containing the row names of the SDF}
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}
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}
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All SDF's created in the session will have their SQLite file stored in the subdirectory .SQLiteDF in the
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current working directory. SDF's created in the other session can be imported/attached
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to the current SDF workspace using \code{attachSdf}, which may reside anywhere in the
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file system.
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}
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}
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\value{
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\value{
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A S3 object representing the SDF. The SDF database will be created in the same directory
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A S3 object representing the SDF. The SDF database will be created in the same directory
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with file name derived by appending the extension \emph{db} to the passed internal
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with file name derived by appending the extension \emph{db} to the passed internal
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name, or the default internal name if none is provided.
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name, or the default internal name if none is provided.