*/** is read by my brain as "Give me everything in this directory and everything in it's directories, then EVERYTHING in all of their nested directories." But by that definition, ** should just give me the entire tree and it is two characters shorter. Since ** does not work this way, my definition is obviously flawed.
Is there an English translation of */** that better describes what it is actually doing?
I'd translate it as "Match all contents recursively of subdirectories of the current directory". The difference from using ** straight away is that this pattern does not match non-directories inside the current directory.
Related
I was teaching an online course and a student asked me why R only uses / and not \ in file paths when using read.csv and other related functions. I tried looking at the documentation but it didn’t really mention anything about it. Never really thought about it because I use a Mac, and the default in Macs is \, but not so in Windows machines.
I’m not trained in computer science so I was left a bit stumped to answer the question a I’m afraid. Students always ask the darnest things!
Interesting question.
First off, the "forward slash" / is actually more common as it used by Unix, Linux, and macOS.
Second, the "backward slash" \ is actually somewhat painful as it is also an escape character. So whenever you want one, you need to type two in string: "C:\\TEMP".
Third, R on Windows knows this and helps! So you can you use a forward slash whereever you would use a backward slash: "C:/TEMP" works the same!
Fourth, you can have R compute the path for you and it will use use the separator: file.path("some", "dir").
So the short answer: R uses both on Windows and lets you pick whichever you find easier. But remember to use two backward slashes (unless you use the very new R 4.0.0 feature on raw strings which I'll skip for now).
(Note: backslashes as directory folder separators on Macs is a recent innovation.See History of Mac folder separators
I think if you review the history (or look it up if you were not there when it occurred as I was) you will find that Unix (which Linux copied completely) got there first. It preceded either MS-DOS or Macs or last of all Windows. R is a work-alike clone of S which was developed like Unix at Bell Labs.
Mac originally used colons (:) as folder separators (and still won't accept them in file names) and converted to slashes sometime during its long transition to BSD Unix which it licensed from ATT.
Shouldn't the question be: why Microsoft chose to use a backslash?
I would like to write a line in a text file at a given position (i) by avoiding the sequential reading.
There is WriteLines base function but I don't know how to insert the text at position (i) given as parameter.
Thanks
Dave
This is — unrelated to R — fundamentally impossible. Most (all common) filesystems do not support inserting or removing content in the middle of a file. The only supported operations are appending (or truncation) at the end, and R only supports appending, not truncation.
The way virtually all software solves your problem is by reading the file, modifying it, and writing it back to disk. If you want to get fancy because the file is very large (at least in the order of hundreds of MiB), you can stream edit the file: Read a part, edit that part, write it back to a new file. Rinse and repeat.
Technical aside: There is one exception to the above with low-level file operations, since files are stored as as non-contiguous “blocks”. But even if R supported this it wouldn’t help you since it doesn’t permit byte-level or line-level granularity: Blocks are typically at least 4 kiB in size.
I have to use Textpad in my environment. To treat a file (on a regular basis) it is necessary to make +/- 20 replacements, some of them regex, some of them not. For most of the replacements I have defined macros (for each replacement one macro, i. e. 1:1). It is possible to "concat" macros or put replacements "in a sequence"? If it is possible: Would this sequence break, if one replacement does not find matching patters (off course, it should not break).
I'm not sure how you would "concat" them aside from recording each macro together (unless you know how to concat the files)... but as your question is about "would it work"... then I'd say yes but you would have to ensure each marco started in the right place.
I'd recommend each macro started and ended with something like Ctrl+Home to ensure a consistent starting / ending place
Is there a new line constant that's platform independent in R? I'm used to C# and there's Environment.NewLine which will return \r\n on windows and \n otherwise. Searching turned up nothing, but I assume there has to be something somewhere so that scripts can be platform independent.
Related question: Is there a way to detect the platform a script is running on? This could be useful to know for other reasons (which I haven't thought of yet).
EDIT: Here's why I'm asking. I'm downloading files from an FTP server, but want to get a list of files and only download files that are on the server that don't exist locally. Here's how I'm getting the list of files:
filesonserver <- unlist(strsplit(getURL(basePath, ftp.use.epsv=F, dirlistonly=T), "\n"))
On windows, the files are separated by \r\n. On my mac (where I'm currently working), they're separated by \n. I was looking for a way to make this platform independent. I haven't tried just separating by \n on windows, which might work. There might also be a way to get the list of files as a vector without having to split them, which would avoid this entirely...
The package tryCatchLog has a function determine.platform.NewLine():
https://cran.r-project.org/package=tryCatchLog
https://github.com/aryoda/tryCatchLog/blob/master/R/platform_newline.R
If you consequently use this string instead of hard-coded "\n" your new lines will work platform-independently.
The answer to the initial question appears to be there isn't a new line constant like C# has. But it doesn't matter in my case, as the comments pointed out. It didn't occur to me until after I edited in the details that I probably didn't need to worry about it. Splitting by \n works fine on windows, even though the string containing the files names returned by getURL() is split by \r\n.
When I organize my directories I often want certain directories to stand out in ls. For example, I will sometimes have a directory called #backup# and this will end up in the top of the list of directories, rather than in between all directories starting in "b". Sometimes, though, I want a directory to be at the bottom of the list, but I haven't found any symbol that achieves this. (The closest I've come is z#name#z, but this doesn't quite cut it.) So: Are there any symbols that come after all letters in Unix's alphabetical sorting?
You can use any (e.g. ASCII or Unicode [it depends upon your encoding and localization]) character except NULL (used as the ending of filepath) and / (used to separate directories in file path). See path_resolution(7). You might consider using ~ because several utilities (see indent(1), mv(1)....) adopt the convention to backup file /home/nag/foo as /home/nag/foo~. AFAIK #foo# could be used by emacs to backup temporarily an edited (but unsaved) file foo.