Hi again,
I have loaded a huge csv file in R using 'ff' package, however could not
understand how can I subset the loaded object. Below is my try:
> suppressMessages(library(ff))
>
> Dat <- read.csv.ffdf(file = "f:/Book1.csv", header = F, colClasses =
c('Date', 'factor'))
> Dat
ffdf (all open) dim=c(4,2), dimorder=c(1,2) row.names=NULL
ffdf virtual mapping
PhysicalName VirtualVmode PhysicalVmode AsIs VirtualIsMatrix
PhysicalIsMatrix PhysicalElementNo PhysicalFirstCol PhysicalLastCol
PhysicalIsOpen
V1 V1 double double FALSE FALSE
FALSE 1 1 1 TRUE
V2 V2 integer integer FALSE FALSE
FALSE 2 1 1 TRUE
ffdf data
V1 V2
1 2013-12-28 a
2 2013-12-28 b
3 2013-12-27 c
4 2013-12-27 c
>
> subset(Dat, Dat$V1 == as.Date('2013-12-27'))
ffdf (all open) dim=c(4,0), dimorder=c(1,2) row.names=NULL
ffdf virtual mapping
[1] PhysicalName VirtualVmode PhysicalVmode AsIs
VirtualIsMatrix PhysicalIsMatrix PhysicalElementNo PhysicalFirstCol
PhysicalLastCol
[10] PhysicalIsOpen
<0 rows> (or 0-length row.names)
ffdf data
[1] "[empty matrix]"
My resulting object is showing '0' rows!
The 'Dat' object looks like below:
> dput(Dat)
structure(list(virtual = structure(list(VirtualVmode = c("double",
"integer"), AsIs = c(FALSE, FALSE), VirtualIsMatrix = c(FALSE,
FALSE), PhysicalIsMatrix = c(FALSE, FALSE), PhysicalElementNo = 1:2,
PhysicalFirstCol = c(1L, 1L), PhysicalLastCol = c(1L, 1L)), .Names =
c("VirtualVmode",
"AsIs", "VirtualIsMatrix", "PhysicalIsMatrix", "PhysicalElementNo",
"PhysicalFirstCol", "PhysicalLastCol"), row.names = c("V1", "V2"
), class = "data.frame", Dim = c(4L, 2L), Dimorder = 1:2), physical =
structure(list(
V1 = structure(list(), physical = <pointer: 0x0298f498>, virtual =
structure(list(), Length = 4L, Symmetric = FALSE, ramclass = "Date"), class
= c("ff_vector",
"ff")), V2 = structure(list(), physical = <pointer: 0x0298f4c8>,
virtual = structure(list(), Length = 4L, Symmetric = FALSE, Levels = c("a",
"b", "c"), ramclass = "factor"), class = c("ff_vector", "ff"
))), .Names = c("V1", "V2")), row.names = NULL), .Names = c("virtual",
"physical", "row.names"), class = "ffdf")
Can experts here guide me how to subset that?
Thanks for your time.
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