patterns {data.table} | R Documentation |
patterns
returns the elements of cols
that match the regular expression patterns, which must be
supported by grep
.
From v1.9.6
, melt.data.table
has an enhanced functionality
in which measure.vars
argument can accept a list of column names
and melt them into separate columns. See the Efficient reshaping using
data.tables
vignette linked below to learn more.
patterns(
..., cols=character(0),
ignore.case=FALSE, perl=FALSE,
fixed=FALSE, useBytes=FALSE)
... |
A set of regular expression patterns. |
cols |
A character vector of names to which each pattern is matched. |
ignore.case , perl , fixed , useBytes |
Passed to |
melt
,
https://github.com/Rdatatable/data.table/wiki/Getting-started
DT = data.table(x1 = 1:5, x2 = 6:10, y1 = letters[1:5], y2 = letters[6:10])
# melt all columns that begin with 'x' & 'y', respectively, into separate columns
melt(DT, measure.vars = patterns("^x", "^y", cols=names(DT)))
# when used with melt, 'cols' is implicitly assumed to be names of input
# data.table, if not provided.
melt(DT, measure.vars = patterns("^x", "^y"))