Transform block constructors

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_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 = "", ...)

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()

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)

Value

All blocks constructed via new_transform_block() inherit from transform_block.

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", "lfet" 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().