Myujth

I have been experimenting for a while now with R in Azure Data Lake Analytics and I keep getting stuck on installaing extra R-packages like dlplyr and tidyr. I asked the following question, but that did not solve the issue: Installing R-packages in Azure Data Lake Analytics

Now I am trying to follow this tutorial https://blog.revolutionanalytics.com/2017/10/adla-with-r.html but get an error when executing the third script usqlscriptEx3a.usql (https://github.com/Azure/ADLAwithR-GettingStarted/tree/master/Tutorial/Exercise3). I am using te script as is and I have been debugging the R-code locally, and that seems to do the right thing, so now I do not know where to look. The error is:

An unhandled exception from user code has been reported when invoking the method 'Reduce' on the user type 'Extension.R.Reducer'
Unhandled exception from user code: "Output column 'Par' is missing from the data frame"

However Par seems to be there as it should be.

Here follows some of the code from usqlscriptEx3a.usql:

REFERENCE ASSEMBLY [ExtR];

//declare the R script as a string variable and pass it as a parameter to 
the Reducer:
DECLARE @myRScript = @"
temp = inputFromUSQL

t1 = loadedNamespaces()
temp = data.frame(loadedNamespaces = t1) 

t2 = data.frame(apply(temp[1],1,FUN=function(x) 
paste(unlist(packageVersion(as.character(x))),collapse='.')) )
names(t2) = 'packageVersion'
temp$packageVersion = t2$packageVersion

t3 = sessionInfo()[1]
t3 = t3$R.version$version.string
t3 = as.character(t3)
temp$Rversion = t3
temp$Rversion[2:nrow(temp)]=''

outputToUSQL = temp
";

DECLARE @myOutputFile string = @"/TutorialMaterial/outex3a.txt";

@somedata = 
SELECT * FROM 
 (VALUES
 ("Contoso", 1500.0),
 ("Woodgrove", 2700.0)
 ) AS 
 D( customer, amount );


@ExtendedData = SELECT 
0 AS Par,
 *
FROM @somedata;


@RScriptOutput = REDUCE @ExtendedData ON Par PRODUCE 
Par, 
loadedNamespaces string,
packageVersion string,
Rversion string 
USING new Extension.R.Reducer(command:@myRScript, rReturnType:"dataframe");

It turns out, that what was missing, at least in my case, is the following line:

READONLY Par

In order to make the script usqlscriptEx3a.usql work I had to insert READONLY Par in the following lines:

@RScriptOutput = REDUCE @ExtendedData ON Par
PRODUCE Par, 
loadedNamespaces string,
packageVersion string,
Rversion string
READONLY Par
USING new Extension.R.Reducer(command:@myRScript, rReturnType:"dataframe");