datadr (version 0.8.4)

divide: Divide a Distributed Data Object

Description

Divide a ddo/ddf object into subsets based on different criteria

Usage

divide(data, by = NULL, spill = 1000000, filterFn = NULL, bsvFn = NULL,
  output = NULL, overwrite = FALSE, preTransFn = NULL,
  postTransFn = NULL, params = NULL, packages = NULL, control = NULL,
  update = FALSE, verbose = TRUE)

Arguments

data

an object of class "ddf" or "ddo" - in the latter case, need to specify preTransFn to coerce each subset into a data frame

by

specification of how to divide the data - conditional (factor-level or shingles), random replicate, or near-exact replicate (to come) -- see details

spill

integer telling the division method how many lines of data should be collected until spilling over into a new key-value pair

filterFn

a function that is applied to each candidate output key-value pair to determine whether it should be (if returns TRUE) part of the resulting division

bsvFn

a function to be applied to each subset that returns a list of between subset variables (BSVs)

output

a "kvConnection" object indicating where the output data should reside (see localDiskConn, hdfsConn). If NULL (default), output will be

overwrite

logical; should existing output location be overwritten? (also can specify overwrite = "backup" to move the existing output to _bak)

preTransFn

a transformation function (if desired) to applied to each subset prior to division - note: this is deprecated - instead use addTransform prior to calling divide

postTransFn

a transformation function (if desired) to apply to each post-division subset

params

a named list of objects external to the input data that are needed in the distributed computing (most should be taken care of automatically such that this is rarely necessary to specify)

packages

a vector of R package names that contain functions used in fn (most should be taken care of automatically such that this is rarely necessary to specify)

control

parameters specifying how the backend should handle things (most-likely parameters to rhwatch in RHIPE) - see rhipeControl and localDiskContr

update

should a MapReduce job be run to obtain additional attributes for the result data prior to returning?

verbose

logical - print messages about what is being done

Value

• an object of class "ddf" if the resulting subsets are data frames. Otherwise, an object of class "ddo".

Details

The division methods this function will support include conditioning variable division for factors (implemented -- see condDiv), conditioning variable division for numerical variables through shingles, random replicate (implemented -- see rrDiv), and near-exact replicate. If by is a vector of variable names, the data will be divided by these variables. Alternatively, this can be specified by e.g. condDiv(c("var1", "var2")).

References

• http://tessera.io
• http://onlinelibrary.wiley.com/doi/10.1002/sta4.7/full{Guha, S., Hafen, R., Rounds, J., Xia, J., Li, J., Xi, B., & Cleveland, W. S. (2012). Large complex data: divide and recombine (D&R) with RHIPE.Stat, 1(1), 53-67.

See Also

recombine, ddo, ddf, condDiv, rrDiv

Examples

# divide iris data by Species by passing in a data frame
bySpecies <- divide(iris, by = "Species")
bySpecies

# divide iris data into random partitioning of ~30 rows per subset
irisRR <- divide(iris, by = rrDiv(30))
irisRR

# any ddf can be passed into divide:
irisRR2 <- divide(bySpecies, by = rrDiv(30))
irisRR2
bySpecies2 <- divide(irisRR2, by = "Species")
bySpecies2

# splitting on multiple columns
byEdSex <- divide(adult, by = c("education", "sex"))
byEdSex
byEdSex[[1]]

# splitting on a numeric variable
bySL <- ddf(iris) %>%
  addTransform(function(x) {
    x$slCut <- cut(x$Sepal.Length, 10)
    x
  }) %>%
  divide(by = "slCut")
bySL
bySL[[1]]