Aggregate Function Argument Not Giving different answers

[sdewees0523]

Hello,

Thank you for all your work on this package. I'm currently using aggregate.stars to get different monthly summary statistics and am consistently getting the same pixel values regardless of the value I pass to the FUN argument. Example from one of your example use cases:

 t1 = as.Date("2018-07-31")
 x = read_stars(c(tif, tif, tif, tif), along = list(time = c(t1, t1+1, t1+2, t1+3)))[,1:30,1:30]
 st_get_dimension_values(x, "time")
x_agg_time_max= aggregate(x, by = t1 + c(0, 2, 4), FUN = max)
x_agg_time_min = aggregage(x, by = t1+ c(0,2,4, FUN = min)
x_agg_time_mean = aggregate(x, by = t1+c(0,2,4, FUN = min)

plot(x_agg_time_max)
plot(x_agg_time_min)
plot(x_agg_time_mean)

Not that all three plots are identical.

Thank you for your help on this!

[edzer]

I think the problem is that in your example, the data sets (time series) over which you compute mean, min and max are constant in all cases. For example:

library(stars)
# Loading required package: abind
# Loading required package: sf
# Linking to GEOS 3.12.2, GDAL 3.11.3, PROJ 9.4.1; sf_use_s2() is TRUE
t1 = as.Date("2018-07-31")
tif = system.file("tif/L7_ETMs.tif", package = "stars")
x = read_stars(c(tif, tif, tif, tif), along = list(time = c(t1, t1+1, t1+2, t1+3)))[,1:30,1:30]
# give the different time steps different values:
x[[1]][,,,2] = x[[1]][,,,2] * 2
x[[1]][,,,3] = x[[1]][,,,3] * 3
x[[1]][,,,4] = x[[1]][,,,4] * 4
st_get_dimension_values(x, "time")
# [1] "2018-07-31" "2018-08-01" "2018-08-02" "2018-08-03"
by = t1 + c(0, 2, 4)
aggregate(x, by, FUN = max)
# stars object with 4 dimensions and 1 attribute
# attribute(s):
#              Min. 1st Qu. Median     Mean 3rd Qu. Max. NA's
# L7_ETMs.tif    34     114    150 172.7639     232  580 5400
# dimension(s):
#      from to     offset  delta                     refsys point x/y
# time    1  3 2018-07-31 2 days                       Date    NA    
# x       1 30     288776   28.5 SIRGAS 2000 / UTM zone 25S FALSE [x]
# y       1 30    9120761  -28.5 SIRGAS 2000 / UTM zone 25S FALSE [y]
# band    1  6         NA     NA                         NA    NA    
aggregate(x, by, FUN = min)
# stars object with 4 dimensions and 1 attribute
# attribute(s):
#              Min. 1st Qu. Median     Mean 3rd Qu. Max. NA's
# L7_ETMs.tif    17      58     87 115.1759     174  435 5400
# dimension(s):
#      from to     offset  delta                     refsys point x/y
# time    1  3 2018-07-31 2 days                       Date    NA    
# x       1 30     288776   28.5 SIRGAS 2000 / UTM zone 25S FALSE [x]
# y       1 30    9120761  -28.5 SIRGAS 2000 / UTM zone 25S FALSE [y]
# band    1  6         NA     NA                         NA    NA    
aggregate(x, by, FUN = mean)
# stars object with 4 dimensions and 1 attribute
# attribute(s):
#              Min. 1st Qu. Median     Mean 3rd Qu.  Max. NA's
# L7_ETMs.tif  25.5      87  118.5 143.9699     203 507.5 5400
# dimension(s):
#      from to     offset  delta                     refsys point x/y
# time    1  3 2018-07-31 2 days                       Date    NA    
# x       1 30     288776   28.5 SIRGAS 2000 / UTM zone 25S FALSE [x]
# y       1 30    9120761  -28.5 SIRGAS 2000 / UTM zone 25S FALSE [y]
# band    1  6         NA     NA                         NA    NA