Dynamically specifying the formula says 'No supported inverse for this function'

[ashraaghav]

Hi, Great work on the package by the way.

I want to generate my formula dynamically from a list of variable names. So I tried to paste them into a string and convert that into a formula. However, this is throwing an error saying "No supported inverse for this function"

Example:

# Preparing the data
airquality %>% mutate(
    date = as.Date(paste('2018', Month, Day, sep = '-')), 
    Ozone = round(imputeTS::na.interpolation(Ozone, option = 'stine')),
    Solar.R = round(imputeTS::na.interpolation(Solar.R, option = 'stine'))
  ) %>% 
  as_tsibble()

# Creating formula
f <- as.formula('y ~ Wind + Temp + Solar.R + trig(12) + poly(1) + ARMA(1, 1)')

# Building fasster without formula parsing
fsModel <- FASSTER(data = train, 
    formula = y ~ Wind + Temp + Solar.R + trig(12) + poly(1) + ARMA(1, 1))

# Building fasster - throws an error 
fsModel <- FASSTER(data = train, formula = f)

I am not sure if I am doing anything wrong here. The same formula when passed directly worked perfectly fine.

[mitchelloharawild]

Working on a fix now, something is not correct with the parsing of the formula.

---

A few changes to your example:

• Ozone should be the response instead of y, it probably worked for you because you had y somewhere in your environment
• ARMA is used with the coefficients for the AR and MA terms, so this would have the AR and MA coefficients both as 1 (unlikely what you intended, but this is something I intend to change).
• Save the prepared data as train

---

library(fasster)
library(fable)
library(tsibble)

# Preparing the data
train <- airquality %>% mutate(
  date = as.Date(paste('2018', Month, Day, sep = '-')), 
  Ozone = round(imputeTS::na.interpolation(Ozone, option = 'stine')),
  Solar.R = round(imputeTS::na.interpolation(Solar.R, option = 'stine'))
) %>% 
  as_tsibble()

# Creating formula
f <- as.formula('Ozone ~ Wind + Temp + Solar.R + trig(12) + poly(1) + ARMA(1, 1)')

# Building fasster without formula parsing
fsModel <- FASSTER(data = train, 
                   formula = Ozone ~ Wind + Temp + Solar.R + trig(12) + poly(1) + ARMA(1, 1))

# Building fasster - throws an error 
fsModel <- FASSTER(data = train, formula = f)

[mitchelloharawild]

Resolved in https://github.com/tidyverts/fable/commit/4e1521f3612e237fa99fa7fcc12321f0f1b8c694

[ashraaghav]

Apologies for the typo. Thanks for the fix!