在最后 X 小时内查找 xts 列中的最大值

Question

I have a dataset within a reactive dygraph that looks like this:

data()$data.o

date	data.o
2022-07-21 12:10 AM	400.1
2022-07-21 12:11 AM	33.9
2022-07-21 12:12 AM	32.5
2022-07-21 12:13 AM	35.1
2022-07-21 12:14 AM	31.5
2022-07-21 12:15 AM	39.5

I want to find the max value in the last 5 minutes so I can set my axis scale accordingly.

I've tried:

enddate = max(data()$date)
startdate = enddate - (60*5)
oMx <- max(datao.xts[startdate/enddate], na.rm = T)

But I get an error using datao.xts.

Is there a better way to go about this?

Answer 1

As far as I'm familiar with xts , your startdate/enddate part has simply to be a string, cf Joshua's response here . That's it.

# allow me to create an xts object beforehand
datetimes <- c("2022-07-21 12:10 AM",
               "2022-07-21 12:11 AM",
               "2022-07-21 12:12 AM",
               "2022-07-21 12:13 AM",
               "2022-07-21 12:14 AM",
               "2022-07-21 12:15 AM") |> 
  strptime(format = "%Y-%m-%d %I:%M %p") |> 
  as.POSIXct()

data <- c(400.1, 33.9, 32.5, 35.1, 31.5, 39.5)

xts <- xts::xts(data, order.by = datetimes)

# minor adjustments to your approach
enddate <- zoo::index(xts) |> max()
startdate <- enddate - (5-1) * 60

xts[paste0(startdate, enddate, sep = "/")] |> max()
#> [1] 39.5

# assuming you are interested in the last five observations
xts |> utils::tail(5) |> max()
#> [1] 39.5