Attempt to allow mmap objects to be used as drop-in replacements for data.frame

[Kevin-Jin]

Append data.frame to the vector of classes of the mmap object in as.mmap.data.frame(). This way, is.data.frame() returns true but S3 generic methods will execute the mmap override instead of the data.frame override.

Override `$`(x, i) operator to return NextMethod(i) if i %in% names(x) || !is.data.frame(x), and return `[[`(x, i) otherwise.

Override the 1D selection operator `[[`(x, i) to return NextMethod(i) if is.character(i) && i %in% names(x), and throw subscript out of bounds if is.data.frame(x) && (is.character(i) && !all(i %in% colnames(x)) || is.numeric(i) && i > x$dim[2]) || !is.data.frame(x) && is.numeric(i) && i > length(x) || i == 0, and return just column i otherwise (or cell i if !is.data.frame(x)).

Override the 2D selection operator `[[`(x, i, j) appropriately.

Change the 1D subset operator `[`(x, i, [...]) to throw undefined columns selected if is.data.frame(x) && (is.character(i) && !all(i %in% colnames(x)) || is.numeric(i) && i > x$dim[2]), and return NA if !is.data.frame(x) && is.numeric(i) && i > length(x), and return just columns i otherwise (or cells i if !is.data.frame(x)). Return an empty data.frame or vector to handle the value of 0 for i.

Change the 2D subset operator `[`(x, i, j, [...]) to throw undefined columns selected if is.character(i) && !all(i %in% colnames(x)) || is.numeric(i) && i > x$dim[2], and return .Call("mmap_extract", i, j, [...]) otherwise (as it currently does). Return an empty data.frame or vector to handle the value of 0 for i or j.

Override as.data.frame.mmap(x) to return NextMethod() if !is.data.frame(x), and return x unaltered otherwise.

Override as.list.mmap(x) to return NextMethod() if !is.data.frame(x), and return as.list(x[]) otherwise.

Override as.matrix.mmap(x) to return NextMethod() if !is.data.frame(x) && (is.null(x$dim) || length(x$dim) != 2), and return as.matrix(x[]) otherwise.

[Kevin-Jin]

Change length.mmap(x) to return length(x$storage.mode) if is.data.frame(x).

[Kevin-Jin]

Throw attempt to select more than one element if length(i) > 1 || length(j) > 1 in `[[`(x,i,j). Throw attempt to select less than one element if length(i)< 1 || length(j) < 1 in `[[`(x,i,j).

[Kevin-Jin]

Support drop parameter for `[`(x,i,j) and exact parameter for `[[`(x,i,j).

[Kevin-Jin]

Make sure `[[` drops names for matrices and data.frames while `[` keeps them.

[Kevin-Jin]

Add support for rbind() as long as the types match with the storage.mode.

[Kevin-Jin]

Support logical values for i and j. Also support nrow×2 numerical and character matrices for i when x is two dimensional or is a data.frame. See ?Extract.

[Kevin-Jin]

Fix problems with passing empty vectors for i or j to `[[`(x, i, j).