collapse (version 1.8.4)

quick-conversion: Quick Data Conversion

Description

Fast, flexible and precise conversion of common data objects, without method dispatch and extensive checks:

• qDF, qDT and qTBL convert vectors, matrices, higher-dimensional arrays and suitable lists to data frame, data.table and tibble, respectively.

• qM converts vectors, higher-dimensional arrays, data frames and suitable lists to matrix.

• mctl and mrtl column- or row-wise convert a matrix to list, data frame or data.table. They are used internally by qDF/qDT/qTBL, dapply, BY, etc…

• qF converts atomic vectors to factor (documented on a separate page).

• as_numeric_factor and as_character_factor convert factors, or all factor columns in a data frame / list, to character or numeric (by converting the levels).

Usage

# Converting between matrices, data frames / tables / tibbles
 qDF(X, row.names.col = FALSE, keep.attr = FALSE, class = "data.frame")
 qDT(X, row.names.col = FALSE, keep.attr = FALSE, class = c("data.table", "data.frame"))
qTBL(X, row.names.col = FALSE, keep.attr = FALSE, class = c("tbl_df","tbl","data.frame"))
  qM(X,                        keep.attr = FALSE, class = NULL)
# Programmer functions: matrix rows or columns to list / DF / DT - fully in C++
mctl(X, names = FALSE, return = "list")
mrtl(X, names = FALSE, return = "list")
# Converting factors or factor columns
  as_numeric_factor(X, keep.attr = TRUE)
as_character_factor(X, keep.attr = TRUE)

Arguments

X

a vector, factor, matrix, higher-dimensional array, data frame or list. mctl and mrtl only accept matrices, as_numeric_factor and as_character_factor only accept factors, data frames or lists.

row.names.col

should a column capturing names or row.names be added? e.g. when converting atomic objects to data frame or data frame to data.table. Can be logical TRUE, which will add a column "row.names" in front, or can supply a name for the column e.g. "variable".

keep.attr

logical. FALSE (default) yields a hard / thorough object conversion: All unnecessary attributes are removed from the object yielding a plain matrix / data.frame / data.table. FALSE yields a soft / minimal object conversion: Only the attributes 'names', 'row.names', 'dim', 'dimnames' and 'levels' are modified in the conversion. Other attributes are preserved. See also class.

class

if a vector of classes is passed here, the converted object will be assigned these classes. If NULL is passed, the default classes are assigned: qM assigns no class, qDF a class "data.frame", and qDT a class c("data.table", "data.frame"). If keep.attr = TRUE and class = NULL and the object already inherits the default classes, further inherited classes are preserved. See Details and the Example.

names

logical. Should the list be named using row/column names from the matrix?

return

an integer or string specifying what to return. The options are:

Int.		String		Description
1		"list"		returns a plain list
2		"data.frame"		returns a plain data.frame
3		"data.table"		returns a plain data.table

Value

qDF - returns a data.frame qDT - returns a data.table qTBL - returns a tibble qM - returns a matrix mctl, mrtl - return a list, data frame or data.table qF - returns a factor as_numeric_factor - returns X with factors converted to numeric variables as_character_factor - returns X with factors converted to character variables

Details

Object conversions using these functions are maximally efficient and involve 3 consecutive steps: (1) Converting the storage mode / dimensions / data of the object, (2) converting / modifying the attributes and (3) modifying the class of the object:

(1) is determined by the choice of function and the optional row.names.col argument to qDF and qDT. Higher-dimensional arrays are converted by expanding the second dimension (adding columns, same as as.matrix, as.data.frame, as.data.table).

(2) is determined by the keep.attr argument: keep.attr = TRUE seeks to preserve the attributes of the object. It's effect is like copying attributes(converted) <- attributes(original), and then modifying the "dim", "dimnames", "names", "row.names" and "levels" attributes as necessitated by the conversion task. keep.attr = FALSE only converts / assigns / removes these attributes and drops all others.

(3) is determined by the class argument: Setting class = "myclass" will yield a converted object of class "myclass", with any other / prior classes being removed by this replacement. Setting class = NULL does NOT mean that a class NULL is assigned (which would remove the class attribute), but rather that the default classes are assigned: qM assigns no class, qDF a class "data.frame", and qDT a class c("data.table", "data.frame"). At this point there is an interaction with keep.attr: If keep.attr = TRUE and class = NULL and the object converted already inherits the respective default classes, then any other inherited classes will also be preserved (with qM(x, keep.attr = TRUE, class = NULL) any class will be preserved if is.matrix(x) evaluates to TRUE.)

The default keep.attr = FALSE ensures hard conversions so that all unnecessary attributes are dropped. Furthermore in qDF/qDT/qTBL the default classes were explicitly assigned. This is to ensure that the default methods apply, even if the user chooses to preserve further attributes. For qM a more lenient default setup was chosen to enable the full preservation of time series matrices with keep.attr = TRUE. If the user wants to keep attributes attached to a matrix but make sure that all default methods work properly, either one of qM(x, keep.attr = TRUE, class = "matrix") or unclass(qM(x, keep.attr = TRUE)) should be employed.

See Also

qF, Collapse Overview

Examples

# NOT RUN {
## Basic Examples
mtcarsM <- qM(mtcars)                   # Matrix from data.frame
mtcarsDT <- qDT(mtcarsM)                # data.table from matrix columns
mtcarsTBL <- qTBL(mtcarsM)              # tibble from matrix columns
head(mrtl(mtcarsM, TRUE, "data.frame")) # data.frame from matrix rows, etc..
head(qDF(mtcarsM, "cars"))              # Adding a row.names column when converting from matrix
head(qDT(mtcars, "cars"))               # Saving row.names when converting data frame to data.table

cylF <- qF(mtcars$cyl)                  # Factor from atomic vector
cylF

# Factor to numeric conversions
identical(mtcars,  as_numeric_factor(dapply(mtcars, qF)))

# }
# NOT RUN {
<!-- % ## Explaining the interaction of keep.attr and class. Consider the time series   EuStockMarkets -->
# }
# NOT RUN {
<!-- % plot() -->
# }