[R-sig-Geo] stars objects and case_when

[Edzer Pebesma]

Thank you for pointing to this possibility, I'll add it to the stars 
docs somewhere.

This works but only slightly adapted, e.g. as

out = read_stars(system.file("tif/L7_ETMs.tif", package = "stars")) %>%
   slice(band, 1) %>%
   setNames("x") %>%
   mutate(x = case_when (x<100 ~ NA_real_,   x>100 & x<150 ~ 2))

where:
- I uses setNames("x") so that the attribute is renamed to "x", and you 
can use x in the case_when expressions (rather than the lengthy 
"L7_ETMs.tif")
- I chnaged NA into NA_real_ : the first RHS of the formulas need to be 
all of the same type; as typeof(NA) is "logical", it breaks on the 
second RHS which returns a numeric; if you would TRUE or FALSE rather 
than 2 in the second case_when formula, using NA would be the right 
thing to do in the first.

The examples of case_when document the need for typed NA in RHS: this is 
intended behavior.


On 9/14/20 4:39 PM, Julian M. Burgos wrote:
> Dear list,
> 
> I am wondering if there is a way to use logical statements to replace values of a stars object, for example the case_when function or some other "tidyverse friendly" approach.  For example, I can do something like this:
> 
> st1 <- read_stars(system.file("tif/L7_ETMs.tif", package = "stars")) %>%
>    slice(band, 1)
> 
> st1[st1 < 100] <- NA
> st1[st1 > 100 & st1 < 150] <- 2
> 
> ... and so for.  But I am wondering if there is a way to do this as part of a pipe, looking something like this:
> 
> st1 <- read_stars(system.file("tif/L7_ETMs.tif", package = "stars")) %>%
>    slice(band, 1) %>%
>    mutate(x <- case_when (x<100 ~ NA,
>                           x>100 & x<150 ~ 2))
> 
> Any ideas?
> 
> Takk,
> 
> Julian
> 
> --
> Julian Mariano Burgos, PhD
> Hafrannsóknastofnun, rannsókna- og ráðgjafarstofnun hafs og vatna/
> Marine and Freshwater Research Institute
> Botnsjávarsviðs / Demersal Division
>    Fornubúðir 5, IS-220 Hafnarfjörður, Iceland
> www.hafogvatn.is
> Sími/Telephone : +354-5752037
> Netfang/Email: julian.burgos using hafogvatn.is
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics
Heisenbergstrasse 2, 48149 Muenster, Germany
Phone: +49 251 8333081