Hi, Is there some alternative to cumsum for chron objects? I have data frames that contain some chron objects that look like this: DateTime 13/10/03 12:30:35 NA NA NA 15/10/03 16:30:05 NA NA ... and I've been trying to replace the NA's so that a date/time sequence is created starting with the preceding available value. Because the number of rows with NA's following each available date/time is unknown, I've split the data frame using: splitdf <- split(df, as.factor(df$DateTime)) so that I can later use lapply to work on each "block" of data. I thought I could use cumsum and set the NA's to the desired interval to create the date/time sequence starting with the first row. However, this function is not defined for chron objects. Does anybody know of alternatives to create such a sequence? Thanks in advance, -- Sebastian P. Luque
On 5/17/05, Sebastian Luque <sluque at mun.ca> wrote:> Hi, > > Is there some alternative to cumsum for chron objects? I have data frames > that contain some chron objects that look like this: > > DateTime > 13/10/03 12:30:35 > NA > NA > NA > 15/10/03 16:30:05 > NA > NA > ... > > and I've been trying to replace the NA's so that a date/time sequence is > created starting with the preceding available value. Because the number of > rows with NA's following each available date/time is unknown, I've split > the data frame using: > > splitdf <- split(df, as.factor(df$DateTime)) > > so that I can later use lapply to work on each "block" of data. I thought > I could use cumsum and set the NA's to the desired interval to create the > date/time sequence starting with the first row. However, this function is > not defined for chron objects. Does anybody know of alternatives to create > such a sequence? >The 'zoo' package has na.locf which stands for Last Occurrence Carried Forward, which is what I believe you want. First let us create some test data, x:> library(chron); library(zoo) > x <- chron(c(1.5, 2, NA, NA, 4, NA)) > x[1] (01/02/70 12:00:00) (01/03/70 00:00:00) (NA NA) [4] (NA NA) (01/05/70 00:00:00) (NA NA)> # na.locf is intended for zoo objects but we can convert > # the chron object to zoo, apply na.locf and convert back:> chron(as.vector(na.locf(zoo(as.vector(x)))))[1] (01/02/70 12:00:00) (01/03/70 00:00:00) (01/03/70 00:00:00) [4] (01/03/70 00:00:00) (01/05/70 00:00:00) (01/05/70 00:00:00)
On 5/17/05, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:> On 5/17/05, Sebastian Luque <sluque at mun.ca> wrote: > > Hi, > > > > Is there some alternative to cumsum for chron objects? I have data frames > > that contain some chron objects that look like this: > > > > DateTime > > 13/10/03 12:30:35 > > NA > > NA > > NA > > 15/10/03 16:30:05 > > NA > > NA > > ... > > > > and I've been trying to replace the NA's so that a date/time sequence is > > created starting with the preceding available value. Because the number of > > rows with NA's following each available date/time is unknown, I've split > > the data frame using: > > > > splitdf <- split(df, as.factor(df$DateTime)) > > > > so that I can later use lapply to work on each "block" of data. I thought > > I could use cumsum and set the NA's to the desired interval to create the > > date/time sequence starting with the first row. However, this function is > > not defined for chron objects. Does anybody know of alternatives to create > > such a sequence? > > > > The 'zoo' package has na.locf which stands for Last Occurrence Carried > Forward, which is what I believe you want. > > First let us create some test data, x: > > > library(chron); library(zoo) > > x <- chron(c(1.5, 2, NA, NA, 4, NA)) > > x > [1] (01/02/70 12:00:00) (01/03/70 00:00:00) (NA NA) > [4] (NA NA) (01/05/70 00:00:00) (NA NA) > > > # na.locf is intended for zoo objects but we can convert > > # the chron object to zoo, apply na.locf and convert back: > > > chron(as.vector(na.locf(zoo(as.vector(x))))) > [1] (01/02/70 12:00:00) (01/03/70 00:00:00) (01/03/70 00:00:00) > [4] (01/03/70 00:00:00) (01/05/70 00:00:00) (01/05/70 00:00:00) >Just to reply to my own post, it can actually be done even more simply: chron(na.locf(as.vector(x))) Also in re-reading my post, I think the O in locf stands for observation rather than occurrence.