Creating a 4-hr time interval using a reference column in R - r

Question

I want to create a 4-hrs interval using a reference column from a data frame. I have a data frame like this one:
species<-"ABC"
ind<-rep(1:4,each=24)
hour<-rep(seq(0,23,by=1),4)
depth<-runif(length(ind),1,50)
df<-data.frame(cbind(species,ind,hour,depth))
df$depth<-as.numeric(df$depth)
What I would like is to create a new column (without changing the information or dimensions of the original data frame) that could look at my hour column (reference column) and based on that value will give me a 4-hrs time interval. For example, if the value from the hour column is between 0 and 3, then the value in new column will be 0; if the value is between 4 and 7 the value in the new column will be 4, and so on... In excel I used to use the floor/ceiling functions for this, but in R they are not exactly the same. Also, if someone has an easier suggestion for this using the original date/time data that could work too. In my original script I used the function as.POSIXct to get the date/time data, and from there my hour column.
I appreciate your help,

Answer 1

what about taking the column of hours, converting it to integers, and using integer division to get the floor? something like this
# convert hour to integer (hour is currently a col of factors)
i <- as.numeric(levels(df$hour))[df$hour]
# make new column
df$interval <- (i %/% 4) * 4

Answer 2

Expanding on my comment, since I think you're ultimately looking for actual dates at some point...
Some sample hourly data:
set.seed(1)
mydata <- data.frame(species = "ABC",
ind = rep(1:4, each=24),
depth = runif(96, 1, 50),
datetime = seq(ISOdate(2000, 1, 1, 0, 0, 0),
by = "1 hour", length.out = 96))
list(head(mydata), tail(mydata))
# [[1]]
# species ind depth datetime
# 1 ABC 1 14.00992 2000-01-01 00:00:00
# 2 ABC 1 19.23407 2000-01-01 01:00:00
# 3 ABC 1 29.06981 2000-01-01 02:00:00
# 4 ABC 1 45.50218 2000-01-01 03:00:00
# 5 ABC 1 10.88241 2000-01-01 04:00:00
# 6 ABC 1 45.02109 2000-01-01 05:00:00
#
# [[2]]
# species ind depth datetime
# 91 ABC 4 12.741841 2000-01-04 18:00:00
# 92 ABC 4 3.887784 2000-01-04 19:00:00
# 93 ABC 4 32.472125 2000-01-04 20:00:00
# 94 ABC 4 43.937191 2000-01-04 21:00:00
# 95 ABC 4 39.166819 2000-01-04 22:00:00
# 96 ABC 4 40.068132 2000-01-04 23:00:00
Transforming that data using cut and format:
mydata <- within(mydata, {
hourclass <- cut(datetime, "4 hours") # Find the intervals
hourfloor <- format(as.POSIXlt(hourclass), "%H") # Display just the "hour"
})
list(head(mydata), tail(mydata))
# [[1]]
# species ind depth datetime hourclass hourfloor
# 1 ABC 1 14.00992 2000-01-01 00:00:00 2000-01-01 00:00:00 00
# 2 ABC 1 19.23407 2000-01-01 01:00:00 2000-01-01 00:00:00 00
# 3 ABC 1 29.06981 2000-01-01 02:00:00 2000-01-01 00:00:00 00
# 4 ABC 1 45.50218 2000-01-01 03:00:00 2000-01-01 00:00:00 00
# 5 ABC 1 10.88241 2000-01-01 04:00:00 2000-01-01 04:00:00 04
# 6 ABC 1 45.02109 2000-01-01 05:00:00 2000-01-01 04:00:00 04
#
# [[2]]
# species ind depth datetime hourclass hourfloor
# 91 ABC 4 12.741841 2000-01-04 18:00:00 2000-01-04 16:00:00 16
# 92 ABC 4 3.887784 2000-01-04 19:00:00 2000-01-04 16:00:00 16
# 93 ABC 4 32.472125 2000-01-04 20:00:00 2000-01-04 20:00:00 20
# 94 ABC 4 43.937191 2000-01-04 21:00:00 2000-01-04 20:00:00 20
# 95 ABC 4 39.166819 2000-01-04 22:00:00 2000-01-04 20:00:00 20
# 96 ABC 4 40.068132 2000-01-04 23:00:00 2000-01-04 20:00:00 20
Note that your new "hourclass" variable is a factor and the new "hourfloor" variable is character, but you can easily change those, even during the within stage.
str(mydata)
# 'data.frame': 96 obs. of 6 variables:
# $ species : Factor w/ 1 level "ABC": 1 1 1 1 1 1 1 1 1 1 ...
# $ ind : int 1 1 1 1 1 1 1 1 1 1 ...
# $ depth : num 14 19.2 29.1 45.5 10.9 ...
# $ datetime : POSIXct, format: "2000-01-01 00:00:00" "2000-01-01 01:00:00" ...
# $ hourclass: Factor w/ 24 levels "2000-01-01 00:00:00",..: 1 1 1 1 2 2 2 2 3 3 ...
# $ hourfloor: chr "00" "00" "00" "00" ...

Answer 3

tip number 1, don't use cbind to create a data.frame with differing type of columns, everything gets coerced to the same type (in this case factor)
findInterval or cut would seem appropriate here.
df <- data.frame(species,ind,hour,depth)
# copy
df2 <- df
df2$fourhour <- c(0,4,8,12,16,20)[findInterval(df$hour, c(0,4,8,12,16,20))]

Answer 4

Though there is probably a simpler way, here is one attempt.
Make your data.frame not using cbind first though, so hour is not a factor but numeric
df <- data.frame(species,ind,hour,depth)
Then:
df$interval <- factor(findInterval(df$hour,seq(0,23,4)),labels=seq(0,23,4))
Result:
> head(df)
species ind hour depth interval
1 ABC 1 0 23.11215 0
2 ABC 1 1 10.63896 0
3 ABC 1 2 18.67615 0
4 ABC 1 3 28.01860 0
5 ABC 1 4 38.25594 4
6 ABC 1 5 30.51363 4
You could also make the labels a bit nicer like:
cutseq <- seq(0,23,4)
df$interval <- factor(
findInterval(df$hour,cutseq),
labels=paste(cutseq,cutseq+3,sep="-")
)
Result:
> head(df)
species ind hour depth interval
1 ABC 1 0 23.11215 0-3
2 ABC 1 1 10.63896 0-3
3 ABC 1 2 18.67615 0-3
4 ABC 1 3 28.01860 0-3
5 ABC 1 4 38.25594 4-7
6 ABC 1 5 30.51363 4-7