[R] Unexpected behaviour when using format(x, scientific = TRUE) on integer vector

[Remo Röthlin]

Dear useRs

I’m encountering an unexpected behaviour when trying to apply format(x, scientific = TRUE) on integer vectors (but not double vectors). 
The resulting string is not formatted in scientific notation, however, using formatC() instead, the result is as expected.

Is this the expected behaviour of format(x, scientific = TRUE)? I haven’t found any information or discussion on a difference in scientific notation between format and formatC.

Both functions are implemented as .Internal() functions in C, and while do_formatC() uses C’s directly built-in capabilities to format, do_format() does additional work.
Unfortunately my knowledge of R internals is not good enough to see why format() treats integers differently in this case.

Warm regards,

Remo

SessionInfo and code to reproduce the issue with output (was also reproduced on Windows 10 x64 R 4.1.0 and RStudio Cloud R 3.6.3 & R 4.0.3):

> sessionInfo()
R version 4.1.0 (2021-05-18)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Big Sur 10.16

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.1/Resources/lib/libRblas.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/4.1/Resources/lib/libRlapack.dylib

locale:
[1] de_CH.UTF-8/de_CH.UTF-8/de_CH.UTF-8/C/de_CH.UTF-8/de_CH.UTF-8

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

loaded via a namespace (and not attached):
[1] compiler_4.1.0
> Sys.getlocale()
[1] "de_CH.UTF-8/de_CH.UTF-8/de_CH.UTF-8/C/de_CH.UTF-8/de_CH.UTF-8"
> 
> numvec <- c(-1.23e4, 1.23e4)
> typeof(numvec) # double
[1] "double"
> 
> intvec <- c(-1.23e4L, 1.23e4L)
> typeof(intvec) # integer
[1] "integer"
> 
> numvec2 <- as.double(intvec)
> identical(numvec, numvec2)
[1] TRUE
> 
> formatC(numvec, format = "e") # Formatted as scientific notation
[1] "-1.2300e+04" "1.2300e+04" 
> format(numvec, scientific = TRUE) # Formatted as scientific notation
[1] "-1.23e+04" " 1.23e+04"
> 
> formatC(intvec, format = "e") # Formatted as scientific notation
[1] "-1.2300e+04" "1.2300e+04" 
> format(intvec, scientific = TRUE) # *Not* formatted as scientific notation
[1] "-12300" " 12300"
> 
> formatC(numvec2, format = "e") # Formatted as scientific notation
[1] "-1.2300e+04" "1.2300e+04" 
> format(numvec2, scientific = TRUE) # Formatted as scientific notation
[1] "-1.23e+04" " 1.23e+04"