new_transform_block: Transform block constructors

Description

Many data transformations are be provided by blocks constructed via new_transform_block(), including examples where a single data.frame is transformed into another (e.g. subset_block), and two or more data.frames are combined (e.g. merge_block or rbind_block).

Usage

new_transform_block(server, ui, class, ctor = sys.parent(), ...)
new_fixed_block(expr, ...)
new_head_block(n = 6L, direction = c("head", "tail"), ...)
new_merge_block(by = character(), all_x = FALSE, all_y = FALSE, ...)
new_rbind_block(...)
new_subset_block(subset = "", select = "", ...)

Value

All blocks constructed via new_transform_block() inherit from transform_block.

Arguments

server: A function returning shiny::moduleServer()
ui: A function with a single argument (ns) returning a shiny.tag
class: Block subclass
ctor: String-valued constructor name or function/frame number (mostly for internal use or when defining constructors for virtual classes)
...: Forwarded to new_transform_block() and new_block()
expr: Quoted expression
n: Number of rows
direction: Either "head" or "tail"
by: Column(s) tp join on
all_x, all_y: Join type, see base::merge()
subset, select: Expressions (passed as strings)

Fixed block

Mainly useful for testing and examples, this block applies a fixed transformation to its data input. No UI elements are exposed and the transformation consequently cannot be parametrized. The quoted expression passed as expr is expected to refer to the input data as data.

Head block

Row-subsetting the first or last n rows of a data.frame (as provided by utils::head() and utils::tail()) is implemented as head_block. This is an example of a block that takes a single data.frame as input and produces a single data.frame as output.

Merge block

Joining together two data.frames, based on a set of index columns, using base::merge() is available as merge_block. Depending on values passed as all_x/all_y the result will correspond to an "inner", "outer", "left" or "right" join. See base::merge() for details. This block class serves as an example for a transform block that takes exactly two data inputs x and y to produce a single data.frame as output.

Row-bind block

Row-wise concatenation of an arbitrary number of data.frames, as performed by base::rbind() is available as an rbind_block. This mainly serves as an example for a variadic block via the "special" ...args block data argument.

Subset block

This block allows to perform row and column subsetting on data.frame objects via base::subset(). Using non-standard evaluation, strings passed as subset/select arguments or entered via shiny UI are turned into language objects by base::parse().