How to use flow variables in R snippet?

Hi guys,

I'm using the R snippet node in KNIME Labs – R (Interactive) repository. I would need your help to do something easy in principle: using a flow variables content as a variable name.

I explain myself better. I have the following working code:,

that builds a linear model using the variable “housecost” as response, present in data. Now I want to generalize the code passing the response variable name (in this case “housecost”) from the outside, inside a flow variable called “response”.

I've tried with this:[["response"]]~.,

but it gave me the following error:

Error in model.frame.default(formula =[["response"]] ~ ., :

variable lengths differ (found for 'X')

In the past a KNIME user suggested me to use this:[[[["response"]]]]~.,

With it I don't get any error. Anyway it seems that the linear model is still not able to take "housecost" as response variable name. Indeed it appears between the other dependent variables.

I attached my workflow. Please, do you have some suggestions?


Hi Gio, 

I have been curious about this for a while now and your question made me finally spend some time looking at it.  The best solution I found, was to create the formula for the call to lm manually by constructing the string first and then converting it to a formula.  I imagine there is a more elgant way to do it, but I could not discover what this is.  


My solution:

target =[["response"]]

formula = paste0(target, "~ ."),


Hi Aaron,

Your solution works perfectly. I really don't mind if it's not "elegant", what's important is that it allows me to generalize my workflows!


Thank you so much for your help.

Hi again Aaron,

I'm sorry if I come back to this issue but I found that although your solution perfectly work with the R lm() function, it does NOT with the lda() nor the qda() ones (the R functions to calculate Linear Discriminant Analysis and Quadratic Discriminant Analysis, respectively).

It gives me the following error:

Error in lda.default(formula, data = : 'x' is not a matrix

Please do you have other suggestions?


I think the formula is still fine, but you need to recast your data frame as a matrix for this kind of model.

For example, you could add the line: = data.matrix(

above your QDA call