[Rd] [External] readChar() could read the whole file by default?

[iuke-tier@ey m@iii@g oii uiow@@edu]

On Fri, 26 Jan 2024, Michael Chirico wrote:

> I am curious why readLines() has a default (n=-1L) to read the full
> file while readChar() has no default for nchars= (i.e., readChar(file)
> is an error). Is there a technical reason for this?
>
> I often[1] see code like paste(readLines(f), collapse="\n") which
> would be better served by readChar(), especially given issues with the
> global string cache I've come across[2]. But lacking the default, the
> replacement might come across less clean.

The string cache seems like a very dark pink herring to me. The fact
that the lines are allocated on the heap might create an issue; the
cache isn't likely to add much to that. In any case I would need to
see a realistic example to convince me this is worth addressing on
performance grounds.

I don't see any reason in principle not to have readChar and readBin
read the entire file if n = -1 (others might) but someone would need
to write a patch to implement that.

Best,

luke

> For my own purposes the incantation readChar(file, file.size(file)) is
> ubiquitous. Taking CRAN code[3] as a sample[4], 41% of readChar()
> calls use either readChar(f, file.info(f)$size) or readChar(f,
> file.size(f))[5].
>
> Thanks for the consideration and feedback,
> Mike C
>
> [1] e.g. a quick search shows O(100) usages in CRAN packages:
> https://github.com/search?q=org%3Acran+%2Fpaste%5B%28%5D%5Cs*readLines%5B%28%5D.*%5B%29%5D%2C%5Cs*collapse%5Cs*%3D%5Cs*%5B%27%22%5D%5B%5C%5C%5D%2F+lang%3AR&type=code,
> and O(1000) usages generally on GitHub:
> https://github.com/search?q=lang%3AR+%2Fpaste%5B%28%5D%5Cs*readLines%5B%28%5D.*%5B%29%5D%2C%5Cs*collapse%5Cs*%3D%5Cs*%5B%27%22%5D%5B%5C%5C%5D%2F+lang%3AR&type=code
> [2] AIUI the readLines() approach "pollutes" the global string cache
> with potentially 1000s/10000s of strings for each line, only to get
> them gc()'d after combining everything with paste(collapse="\n")
> [3] The mirror on GitHub, which includes archived packages as well as
> current (well, eventually-consistent) versions.
> [4] Note that usage in packages is likely not representative of usage
> in scripts, e.g. I often saw readChar(f, 1), or eol-finders like
> readChar(f, 500) + grep("[\n\r]"), which makes more sense to me as
> something to find in package internals than in analysis scripts. FWIW
> I searched an internal codebase (scripts and packages) and found 70%
> of usages reading the full file.
> [5] repro: https://gist.github.com/MichaelChirico/247ea9500460dca239f031e74bdcf76b
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>
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-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
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