问题
OpenCPU is said to support chaining of function calls to calculate e.g. f(g(x), h(y))
The docs about argument formats: https://public.opencpu.org/api.html#api-arguments includes an example that illustrates this by calculating
summary(read.csv("mydata.csv"))
In this example f is the generic function summary that takes as an argument an object.
I need to calculate something like:
mycalc(read.csv("mydata.csv"))
or
myplot(read.csv("my data.csv"))
where f takes as an argument a dataframe. This doesn't seem to work when giving as object argument the sessionid or hash key returned by the read.csv function. How can this chaining of two nongeneric functions be solved ?
Here is a complete example:
prepare package to test f(g(x)) here plotcars(dfcars()) in R
dfcars<-function(){
data(cars);
cars
}
plotcars<-function(df){
matplot(1:nrow(df),df)
}
plotcars(dfcars()) # test the two chained functions are working
package.skeleton(list = c("dfcars", "plotcars"), name = "mypkg")
install the new package from the ubuntu terminal
sudo R CMD INSTALL mypkg
Execute function chaining commands as in opencpu docs
curl http://localhost/ocpu/library/mypkg/R/dfcars -d ""
/ocpu/tmp/x07a1f83f/R/.val
/ocpu/tmp/x07a1f83f/stdout
/ocpu/tmp/x07a1f83f/source
/ocpu/tmp/x07a1f83f/console
/ocpu/tmp/x07a1f83f/info
'#replace session id with returned one above
curl http://localhost/ocpu/tmp/x07a1f83f/R/.val/print
speed dist
1 4 2
2 4 10
3 7 4
'# POST chaining with the generic function summary works
curl http://localhost/ocpu/library/base/R/summary -d 'object=x07a1f83f'
/ocpu/tmp/x0e29fd5c/R/.val
/ocpu/tmp/x0e29fd5c/stdout
/ocpu/tmp/x0e29fd5c/source
/ocpu/tmp/x0e29fd5c/console
/ocpu/tmp/x0e29fd5c/info
# and the summary gets printed
curl http://localhost/ocpu/tmp/x0e29fd5c/R/.val/print
speed dist
Min. : 4.0 Min. : 2.00
1st Qu.:12.0 1st Qu.: 26.00
Median :15.0 Median : 36.00
Mean :15.4 Mean : 42.98
3rd Qu.:19.0 3rd Qu.: 56.00
Max. :25.0 Max. :120.00
# POST chaining with the nongeneric function plotcars doesn't work
curl http://localhost/ocpu/library/mypkg/R/plotcars -d 'object=x07a1f83f'
unused argument (object = object)
In call:
plotcars(object = object)
回答1:
From the example it seems you are passing the argument named object
whereas your function has an argument named df
? Performing a POST on a function will map the arguments of the http request to the function parameters. So what you are doing currently is plotcars(object=dfcars())
which results in the error that you see. Try:
curl http://localhost/ocpu/library/mypkg/R/plotcars -d 'df=x07a1f83f'
来源:https://stackoverflow.com/questions/18551069/how-to-chain-two-function-calls-in-opencpu