Dear list,
I have a large dataset which is structured as follows:
locality=c("USC00020958", "USC00020958", "USC00020958", "USC00020958",
"USC00020958", "USC00021001","USC00021001", "USC00021001", "USC00021001",
"USC00021001", "USC00021001")
temp.a=c(-1.2, -1.2, -1.2, -1.2, -1.1, -2.2, -2.4, -2.6,-2.7, -2.8, -3.0)
month= c(12, 12, 12, 12, 12, 11, 11, 11, 11, 11, 11)
day= c(27, 28, 29, 30, 31, 1, 2, 3, 4, 5, 6)
df=data.frame(locality,temp.a,month,day)
> locality temp.a month day
>1 USC00020958 -1.2 12 27
>2 USC00020958 -1.2 12 28
>3 USC00020958 -1.2 12 29
>4 USC00020958 -1.2 12 30
>5 USC00020958 -1.1 12 31
>6 USC00021001 -2.2 11 1
>7 USC00021001 -2.4 11 2
>8 USC00021001 -2.6 11 3
>9 USC00021001 -2.7 11 4
>10 USC00021001 -2.8 11 5
>11 USC00021001 -3.0 11 6
I would like to calculate a 5th variable, temp.t, based on temp.a, and
temp.t for the preceding time step. I successfully created a for loop as
follows:
temp.t=list()
for(i in 2:nrow(df)){
k=0.8
temp.t[1]=df$temp.a[1]
temp.t[i]=(as.numeric(temp.t[i-1]))+k*(as.numeric(df$temp.a[i])-(as.numeric(temp.t[i-1])))
}
temp.t <- unlist(temp.t)
df["temp.t"] <- round(temp.t,1)
df
> locality temp.a month day temp.t
>1 USC00020958 -1.2 12 27 -1.2
>2 USC00020958 -1.2 12 28 -1.2
>3 USC00020958 -1.2 12 29 -1.2
>4 USC00020958 -1.2 12 30 -1.2
>5 USC00020958 -1.1 12 31 -1.1
>6 USC00021001 -2.2 11 1 -2.0
>7 USC00021001 -2.4 11 2 -2.3
>8 USC00021001 -2.6 11 3 -2.5
>9 USC00021001 -2.7 11 4 -2.7
>10 USC00021001 -2.8 11 5 -2.8
>11 USC00021001 -3.0 11 6 -3.0
This worked fine as long as I was dealing with datasets that only
contained one locality. However, as you can see above, my current dataset
contains more than one locality, and I need to execute my loop for each
locality separately. What is the best approach to do this?
I have tried repeatedly to put the loop into a command using either ave,
by or tapply and to specify locality as the grouping variable, but no
matter what I try, nothing works, because I am unable to specify my loop
as a function within ave, by, or tapply.
I don't know if I am just doing it wrong (likely!) since I have no
experience working with loops/functions, or if this is simply not the
right approach to solve my problem. I was also considering using a nested
for loop, but failed at setting it up. I would greatly appreciate if
someone could point me in the right direction.
Thanks a lot,
Stephanie
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
