# [ncl-talk] How to calculate the mean over time dimension with a stride?

Xueyan Zhang xueyanzhang520 at gmail.com
Sun Oct 13 10:53:57 MDT 2019

```Hi ncl_talk,

I have a variable like this:
dimensions:
time = 2920 ;
lat = 224 ;
lon = 464 ;
variables:
float time(time) ;
time:calendar = "noleap" ;
time:long_name = "observation time" ;
time:units = "days since 2098-01-01 00:00:00" ;
float lat(lat) ;
lat:long_name = "latitude                 " ;
lat:units = "degrees_north  " ;
float lon(lon) ;
lon:long_name = "longitude                " ;
lon:units = "degrees_east   " ;
float pr(time, lat, lon) ;
pr:long_name = "Precipitation" ;
pr:units = "mm" ;
pr:_FillValue = 1.e+20f ;

the time value is 0,0.125..364.875
I want to calculate the mean value of pr among time dimension but using
every 8 time index, like pr_mean (0) = (pr(0,:,:)+ pr(1,:,:)+ pr(2,:,:)+
pr(3,:,:)+ pr(4,:,:)+ pr(5,:,:)+ pr(6,:,:)+ pr(7,:,:))/8

I only thought about using loops but it is too slow. Any ideas?

Thanks!

Xueyan
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