R help - Mar 2017 - Extracting time-series data from netCDF file for a defined period using ncdf4 package

Dear All,

I am trying to extract a time series  from a netCDF file.

I want to extract data for the time period  1971-1  to 1990-12-31 only.

time axis units is  'days since 1850-1-1'

For one or two files I can use "count" argument,  but I have more than
100
such files and its time units are different.

Is there any easy way to extract the particular time period using ncdf4
package?

Thank you in advance.

-- 
DILEEPKUMAR. R
J R F, IIT DELHI

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Hi,

You problem as stated certainly is puzzling since you have one NCDF file but
'time units are different'.  I don't know what to make of that.

If you had a simpler case where data are dimensioned as [x,y,t] then you can
convert dates to index use in ncdf4::ncvar_get()

I would start with a look-up-table of the dates in the file.

lut <- seq(from = as.Date("1850-01-01"), to = as.Date(Sys.Date()),
by = 'day')

The use base::findInterval() to convert your start/stop dates to indices. 

mine <- as.Date(c("1971-01-01", "1990-03-01"))

startstop <- findInterval(mine, lut)


Is that at all close to what you seek?
Ben




> On Mar 23, 2017, at 6:07 AM, ???????? kunjaai <dileepkunjaai at
gmail.com> wrote:
> 
> Dear All,
> 
> I am trying to extract a time series  from a netCDF file.
> 
> I want to extract data for the time period  1971-1  to 1990-12-31 only.
> 
> time axis units is  'days since 1850-1-1'
> 
> For one or two files I can use "count" argument,  but I have more
than 100
> such files and its time units are different.
> 
> Is there any easy way to extract the particular time period using ncdf4
> package?
> 
> Thank you in advance.
> 
> -- 
> DILEEPKUMAR. R
> J R F, IIT DELHI
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org