[R] Convert date to continuous variable in R

[Ahmed Attia]

How can I convert date to continuous variable staring from 1. I tried
as.numeric but R starts counting from default January 1, 1970 while my data
start Oct 7, 2009.

I need to do this conversion to plot the date on two x-axes (1 and 3).
Ex;
Date LAI
10/7/2009 0
10/8/2009 0.004173
10/9/2009 0.009997
10/10/2009 0.009998
10/11/2009 0.009999
10/12/2009 0.009999
10/13/2009 0.009999
10/14/2009 0.009999
10/15/2009 0.009998
10/16/2009 0.009998
10/17/2009 0.009998
10/18/2009 0.009998
10/19/2009 0.009998
10/20/2009 0.009998

LAI_simulation$Date <- as.Date( LAI_simulation$Date, '%Y/%m/%d')
plot(LAI~Date, data=LAI_simulation)
LAI_simulation$Date<- as.numeric(LAI_simulation$Date,origin="2009-10-07")
#R does not see the origin
axis.Date(side=3,at=LAI_simulation$Date)




Ahmed Attia, Ph.D.
Agronomist & Soil Scientist

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