compatibility issue of magrittr and arima in R

Question

consider the following example:

library(tidyverse)
set.seed(1)
forecast::forecast
x <- cumsum(rnorm(10))
y1 <- arima(x, order = c(1, 0, 0))
y2 <- x %>% arima(order = c(1, 0, 0))

length(fitted(y1))
[1] 10
length(fitted(y2))
[1] 0

The objects y1and y2are almost identical, the only exceptions being the slots calland series. So I guess that is where the fitted functions starts its magic.

I would really like to work with y1 instead of y2. Does anyone know an alternative function to fitted which produces the same result?

EDIT2: The above "bug" does not appear if the forecast package is not loaded into namespace (via eg. forecast::forecast). I wasnt aware that loading a package into namespace changes the behaviour of some functions.

EDIT: since the code seems not to be reproducible I add my `sessionInfo()´

R version 3.5.2 (2018-12-20)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

Matrix products: default

locale:
[1] LC_COLLATE=German_Austria.1252  LC_CTYPE=German_Austria.1252    LC_MONETARY=German_Austria.1252 LC_NUMERIC=C                    LC_TIME=German_Austria.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] forcats_0.4.0   stringr_1.3.1   dplyr_0.8.0.1   purrr_0.3.0     readr_1.3.1     tidyr_0.8.2     tibble_2.0.1    ggplot2_3.1.0   tidyverse_1.2.1 magrittr_1.5   

loaded via a namespace (and not attached):
 [1] zoo_1.8-4         tidyselect_0.2.5  urca_1.3-0        aTSA_3.1.2        haven_2.0.0       lattice_0.20-38   colorspace_1.4-0  generics_0.0.2    yaml_2.2.0        utf8_1.1.4        rlang_0.3.1       pillar_1.3.1     
[13] withr_2.1.2       glue_1.3.0        forecast_8.5      TTR_0.23-4        modelr_0.1.2      readxl_1.2.0      plyr_1.8.4        quantmod_0.4-13   timeDate_3043.102 munsell_0.5.0     gtable_0.2.0      cellranger_1.1.0 
[25] rvest_0.3.2       tseries_0.10-46   lmtest_0.9-36     parallel_3.5.2    curl_3.3          fansi_0.4.0       broom_0.5.1       xts_0.11-2        Rcpp_1.0.0        scales_1.0.0      backports_1.1.3   jsonlite_1.6     
[37] fracdiff_1.4-2    hms_0.4.2         stringi_1.3.1     grid_3.5.2        cli_1.0.1         quadprog_1.5-5    tools_3.5.2       lazyeval_0.2.1    crayon_1.3.4      pkgconfig_2.0.2   xml2_1.2.0        lubridate_1.7.4 

Answer 1

What you've identified is a problem caused by non-standard evaluation, which is briefly mentioned in the technical note about the magrittr pipe:

The magrittr pipe operators use non-standard evaluation. They capture their inputs and examines them to figure out how to proceed. First a function is produced from all of the individual right-hand side expressions, and then the result is obtained by applying this function to the left-hand side. For most purposes, one can disregard the subtle aspects of magrittr's evaluation, but some functions may capture their calling environment, and thus using the operators will not be exactly equivalent to the "standard call" without pipe-operators.

If you look at the source for arima version of fitted you can see that you were correct in thinking that the call attribute is essential to the method's operation:

getAnywhere(fitted.Arima)
A single object matching ‘fitted.Arima’ was found
It was found in the following places
  registered S3 method for fitted from namespace TSA
  namespace:TSA
with value

function (object, ...) 
{
    fitted = eval(object$call$x) - object$residuals
    fitted
}
<bytecode: 0x000000001e8ff4d8>
<environment: namespace:TSA>