[R] halting with errors

[Nick Wray]

Hello  I am downloading flow data from the UK national river flow archive
(NRFA).  I have code which works (thanks to previous help on r-help) but
the problem is that before I make a call for the data for that particular
year I don’t know whether the data exists for that particular year and
catchment

This is a typical url  and it works if you paste it into the top line on a
web page.  15007 is the code for the Pitnacree catchment in Scotland

https://timeseries.sepa.org.uk/KiWIS/KiWIS?service=kisters&type=queryServices&datasource=0&request=getTimeseriesValues&ts_path=1/15007/Q/15m.Cmd&from=2015-01-01&to=2015-01-31&returnfields=Timestamp,Value,Quality%20Code

It works in R as well with

page<-read_html("
https://timeseries.sepa.org.uk/KiWIS/KiWIS?service=kisters&type=queryServices&datasource=0&request=getTimeseriesValues&ts_path=1/15007/Q/15m.Cmd&from=2015-01-01&to=2015-01-31&returnfields=Timestamp,Value,Quality%20Code
")

    yiq<-page |>

      html_element("table") |>

      html_table(header = TRUE) |>

      (\(x) {

        hdr <- unlist(x[3, ])

        y <- x[-(1:3), ]

        names(y) <- hdr

        y

      })()

        print(nrow(yiq))

    yiq



But if I try to move onto another catchment Kenmore 15006

eg



https://timeseries.sepa.org.uk/KiWIS/KiWIS?service=kisters&type=queryServices&datasource=0&request=getTimeseriesValues&ts_path=1/15016/Q/15m.Cmd&from=2015-01-01&to=2015-01-31&returnfields=Timestamp,Value,Quality%20Code

So in R

read_html(“
https://timeseries.sepa.org.uk/KiWIS/KiWIS?service=kisters&type=queryServices&datasource=0&request=getTimeseriesValues&ts_path=1/15016/Q/15m.Cmd&from=2015-01-01&to=2015-01-31&returnfields=Timestamp,Value,Quality%20Code
”)

This doesn’t work because there’s no data for this catchment for this year

I am pasting in different years (from say 1961 to 2017) in a loop (and this
works if the data sets exist) but the problem is that if the data is not
there (and there doesn’t seem to be a way of determining this elsewhere)
and so there’s nothing to read, an error message comes up and halts the
program loop, so that manually I have to reset the url to try to find out
whether there is data for the next year.

What I’d like to know is whether there’s any way in R of seeing whether the
data set exists, and if doesn’t, moving on the next possibility without
halting…

Any thoughts appreciated

Thanks Nick Wray

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