The zoo package in R allows you to work with time series that have unevenly spaced time intervals, and variable frequencies (no need to interpolate data). The {mblm} package does a Thiel-Sen regression on time-series-like data. Looking at your dummy data I assume that you want to do the regression for each month. Try this:
a <- "
year month day chickens
2000 1 2 1
2000 1 5 2
2000 1 8 3
2000 1 11 4
2000 1 14 5
2000 1 17 6
2000 1 20 7
2000 1 23 8
2000 1 26 9
2000 2 3 2
2000 2 6 4
2000 2 9 6
2000 2 12 8
2000 2 15 10
2000 2 18 12
2000 2 21 14
2000 2 24 16
2000 2 27 18
2000 3 1 3
2000 3 4 6
2000 3 7 9
2000 3 10 12
2000 3 13 15
2000 3 16 18
2000 3 19 21
2000 3 22 24
2000 3 25 27
2000 3 28 30
2000 4 3 4
2000 4 6 8
2000 4 9 12
2000 4 12 16
2000 4 15 20
2000 4 18 24
2000 4 21 28
2000 4 24 32
2000 4 27 36
2000 5 3 5
2000 5 6 10
2000 5 9 15
2000 5 12 20
2000 5 15 25
2000 5 18 30
2000 5 21 35
2000 5 24 40
2000 5 27 45
2000 6 3 6
2000 6 6 12
2000 6 9 18
2000 6 12 24
2000 6 15 30
2000 6 18 36
2000 6 21 42
2000 6 24 48
2000 6 27 54
2000 7 3 7
2000 7 6 14
2000 7 9 21
2000 7 12 28
2000 7 15 35
2000 7 18 42
2000 7 21 49
2000 7 24 56
2000 7 27 63
2000 8 3 8
2000 8 6 16
2000 8 9 24
2000 8 12 32
2000 8 15 40
2000 8 18 48
2000 8 21 56
2000 8 24 64
2000 8 27 72
2000 9 3 9
2000 9 6 18
2000 9 9 27
2000 9 12 36
2000 9 15 45
2000 9 18 54
2000 9 21 63
2000 9 24 72
2000 9 27 81
2000 10 3 10
2000 10 6 20
2000 10 9 30
2000 10 12 40
2000 10 15 50
2000 10 18 60
2000 10 21 70
2000 10 24 80
2000 10 27 90
2000 11 3 11
2000 11 6 22
2000 11 9 33
2000 11 12 44
2000 11 15 55
2000 11 18 66
2000 11 21 77
2000 11 24 88
2000 11 27 99
2000 12 6 12
2000 12 9 24
2000 12 12 36
2000 12 18 48
2000 12 21 60
2000 12 24 72
2000 12 27 84"
df <- read.delim(text=a, header=TRUE)
# making a date column
df$date <- as.Date(with(df, paste(year, month, day,sep="/")), "%Y/%m/%d")
library(zoo)
library(mblm)
for(ii in 1:12) {
tmp <- df[df$month==ii,]
print(tmp)
zz <- zoo(tmp$chickens, tmp$date)
plot(zz, type="b")
fit <- mblm(chickens ~ day, dataframe=tmp)
print(summary(fit))
}
It's a for() loop, I know, but I'll leave someone else to get a nice dplyr or lapply() version working.
HTH