reading_data_II.pdf

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Reading and Writing Data Part II
Roger D. Peng, Associate Professor of Biostatistics
Johns Hopkins Bloomberg School of Public Health
Textual Formats
·
dumping
and dputing are useful because the resulting textual format is edit-able, and in the case
of corruption, potentially recoverable.
·
Unlike
writing out a table or csv file,
dump
and
dput
preserve the
metadata
(sacrificing some
readability), so that another user doesn’t have to specify it all over again.
·
Textual
formats can work much better with version control programs like subversion or git which
can only track changes meaningfully in text files
·
Textual formats can be longer-lived; if there is corruption somewhere in the file, it can be easier to
fix the problem
·
Textual formats adhere to the “Unix philosophy”
·
Downside: The format is not very space-efficient
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dput-ting R Objects
Another way to pass data around is by deparsing the R object with dput and reading it back in using
dget
.
> y <- data.frame(a =
1,
b =
"a")
> dput(y)
structure(list(a =
1,
b = structure(1L, .Label =
"a",
class =
"factor")),
.Names = c("a",
"b"),
row.names = c(NA, -1L),
class =
"data.frame")
> dput(y, file =
"y.R")
> new.y <- dget("y.R")
> new.y
a b
1 1
a
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Dumping R Objects
Multiple objects can be deparsed using the dump function and read back in using
source
.
>
>
>
>
>
>
x <-
"foo"
y <- data.frame(a =
1,
b =
"a")
dump(c("x",
"y"),
file =
"data.R")
rm(x, y)
source("data.R")
y
a b
1 1
a
> x
[1]
"foo"
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Interfaces to the Outside World
Data are read in using
connection
interfaces. Connections can be made to files (most common) or to
other more exotic things.
·
file
, opens a connection to a file
·
gzfile
, opens a connection to a file compressed with gzip
·
bzfile
, opens a connection to a file compressed with bzip2
·
url
, opens a connection to a webpage
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