Standard deviation

[tcalegario]

Dear,

Thanks for this package. Its so fast.

There is a way to evaluate standard deviation, range and median with this package?

Thanks a lot

Best wishes

[tcalegario]

exact_extract(raster, poly, function(values, coverage_fraction) sd(values, na.rm=TRUE))

Is it right?

[dbaston]

Is it right?

That will give you the sample standard deviation, not taking cell coverage fractions into account. You may also want to investigate exact_extract(raster, poly, 'stdev') which will give you the population standard deviation, taking cell coverage fractions into account. This avoids passing all of the pixel values to an R function, so it can work on rasters/polygons of any size without excessive memory usage. You'd need to pull the latest version from GitHub for this to work (it's not yet supported in the CRAN version)

You can calculate range from min & max (exact_extract(raster, poly, c('min', 'max'))).

I haven't implemented median directly, since there isn't an exact way to do it without storing all pixel values in memory. But you can use the R function exact_extract(raster, poly, function(values, coverage_fraction) median(values, na.rm)) although it does not take cell coverage fraction into account.

[tcalegario]

Dear dbaston

Thanks a lot.

This package is awesome. I`m sharing with all my worknet.

By GitHub version, you mean that available in this link?

https://github.com/isciences/exactextractr

Best regards

A.

[dbaston]

Thanks! Yes, you can install it from GitHub with remotes::install_github('isciences/exactextractr'). Eventually I'll update the version on CRAN to include the standard deviation.

[tcalegario]

I installed it but didn`t recognize the function "stdev"

install.packages("isciences/exactextractr")

exact_extract(raster, poli, fun = c("mean", "stdev","max", "min"))

As result:

r in CPP_stats(x, weights, wkb, fun, max_cells_in_memory) : Unknown stat: stdev In addition: Warning message: In .local(x, y, ...) : Polygons transformed to raster CRS (EPSG:NA)

[dbaston]

install.packages installs from CRAN; use remotes::install_github('isciences/exactextractr')

[tcalegario]

LoL!

Noob mistake.

Thanks man!!

[tcalegario]

I uninstalled exactextract from R and installed it again using your code (version 0.4.0).

Result was the same. :/

Do you know what may be the problem?