While running an R-plugin in SPSS, I receive a Windows path string as input e.g.
'C:\Users\mhermans\somefile.csv'
I would like to use that path in subsequent R code, but then the slashes need to be replaced with forward slashes, otherwise R interprets it as escapes (eg. "\U used without hex digits" errors).
I have however not been able to find a function that can replace the backslashes with foward slashes or double escape them. All those functions assume those characters are escaped.
So, is there something along the lines of:
>gsub('\\', '/', 'C:\Users\mhermans')
C:/Users/mhermans
You can try to use the 'allowEscapes' argument in scan()
X=scan(what="character",allowEscapes=F)
C:\Users\mhermans\somefile.csv
print(X)
[1] "C:\\Users\\mhermans\\somefile.csv"
As of version 4.0, introduced in April 2020, R provides a syntax for specifying raw strings. The string in the example can be written as:
path <- r"(C:\Users\mhermans\somefile.csv)"
From ?Quotes:
Raw character constants are also available using a syntax similar to the one used in C++: r"(...)" with ... any character sequence, except that it must not contain the closing sequence )". The delimiter pairs [] and {} can also be used, and R can be used in place of r. For additional flexibility, a number of dashes can be placed between the opening quote and the opening delimiter, as long as the same number of dashes appear between the closing delimiter and the closing quote.
First you need to get it assigned to a name:
pathname <- 'C:\\Users\\mhermans\\somefile.csv'
Notice that in order to get it into a name vector you needed to double them all, which gives a hint about how you could use regex. Actually, if you read it in from a text file, then R will do all the doubling for you. Mind you it not really doubling the backslashes. It is being stored as a single backslash, but it's being displayed like that and needs to be input like that from the console. Otherwise the R interpreter tries (and often fails) to turn it into a special character. And to compound the problem, regex uses the backslash as an escape as well. So to detect an escape with grep or sub or gsub you need to quadruple the backslashes
gsub("\\\\", "/", pathname)
# [1] "C:/Users/mhermans/somefile.csv"
You needed to doubly "double" the backslashes. The first of each couple of \'s is to signal to the grep machine that what next comes is a literal.
Consider:
nchar("\\A")
# returns `[1] 2`
If file E:\Data\junk.txt contains the following text (without quotes): C:\Users\mhermans\somefile.csv
You may get a warning with the following statement, but it will work:
texinp <- readLines("E:\\Data\\junk.txt")
If file E:\Data\junk.txt contains the following text (with quotes): "C:\Users\mhermans\somefile.csv"
The above readlines statement might also give you a warning, but will now contain:
"\"C:\Users\mhermans\somefile.csv\""
So, to get what you want, make sure there aren't quotes in the incoming file, and use:
texinp <- suppressWarnings(readLines("E:\\Data\\junk.txt"))
Related
i would like to create a string in the following exact format :
"\"\"\"\nThis is a beautiful world.\n"
But the code :
test ="\"\"\"\nthis is a beautiful world.\n"
test
gives the output :
'"""\nthis is a beautiful world.'
please help in getting an exact text.
My string test should look exactly like the string it has been initialized to. but after initialization, it actually gives the output as mentioned. i want to concatenate the test string to another string
the symbol "\" is called an escape character in most programming languages. this is used to add symbols to a string that might not be easy to add. eg - to add a double quote into a string, we add the \" to the string. eg -
a = "he said, \"hello\" to me"
this would give the output as -
he said "hello" to me
here, the "\" acts as a symbol for the code which allows it to recognize characters which might raise errors other-wise.
to include a backslash in your code, add an extra backslash to it. eg -
a = "\\"
here, the value of a is \.
if you still haven't been able to understand it, try - this tutorial
for your code,try this -
test = "\\\"\\\"\\\"\\nThis is a beautiful world.\\n"
and if you also want the double quotes at the ends,
test = "\"\\\"\\\"\\\"\\nThis is a beautiful world.\\n\""
The first thing to note is, that just typing in the variable name when running python interactively returns the canonical string representation of the object and not (necessarily) the plain value of the object.
For strings this means (among other things) that quotes are added around the output (in your example the outermost single quotes) and any newlines are replaced with "\n".
This means that, although your output does show "\n" the actual string contains a newline character in its place.
The check what a string looks like, you should use the print() function to, well, print it.
>>> test = "\"\"\"\nthis is a beautiful world."
>>> test
'"""\nthis is a beautiful world.'
>>> print(test)
"""
this is a beautiful world.
>>>
Also, when running the code from a file, lines just containing variable names will not result in any output.
To answer the question
There are a few ways to handle that.
Assuming that the desired output is
"""\nThis is a beautiful world.\n
i.e. the outermost double quotes are not supposed to be part of the string, that is
While using double quotes ("…") to denote strings: escape any \ or " by prepending it with \:
>>> test ="\\\"\\\"\\\"\\nthis is a beautiful world.\\n"
>>> print(test)
\"\"\"\nthis is a beautiful world.\n
Within regular strings \ is used to designate control character. For example: \n is interpreted as newline, \b would be a backspace. If you need to have a \ in a string, you need actually write two \\.
If you are usually using "…" for string notation, this allows for a more consistent coding style but it is (especially in this case) quite ugly and might be hard to understand at a glance.
As your string contains a lot of " characters, just use single quotes ('…') to designate the string. This removes the need to escape ":
>>> test = '\\"\\"\\"\\nthis is a beautiful world.\\n'
>>> print(test)
\"\"\"\nthis is a beautiful world.\n
This is less consistent (if "…" is usually used for strings, but allows the code to be quite a bit closer to the desired output.
Use raw strings (r'…' or r"…") to disable the interpretation of control characters and allow the use of " within the string:
>>> test = r'\"\"\"\nthis is a beautiful world.\n'
>>> print(test)
\"\"\"\nthis is a beautiful world.\n"
or even
>>> test = r"\"\"\"\nthis is a beautiful world.\n"
>>> print(test)
\"\"\"\nthis is a beautiful world.\n"
This allows the code to be identical to the desired output, but it has some limitations when it comes to freely mixing " and ' within a single string as it is not possible to escape the quotation marks within the string without also adding \ to the string output. This can be seen in the second example, where we use \" to escape the double quote within r"…" in the code but where the \s are still present in the output. While this works well in this specific case, I would recommend against using \' within r'…' or \" within r"…" to avoid confusion.
I have a string looks like this:
(The whole code block is a string, aka, this string contains quotation marks.)
"he\"llo", "world\n", "fro,m"
[update] Aka, the "actual" string is this:
"\"he\\\"llo\", \"world\\n\", \"fro,m\""
I want to get an array of strings like this:
[ "\"he\\\"llo\"", "\"world\\n\"", "\"fro,m\"" ]
[update] Comma inside quotation marks should be remained.
In my opinion, there are several ways to solve this:
build a automata (DFA or NFA) for this syntax
using several status flags like inQuote, handle judging logics with lots of if else
write a complex but clever Regular Expression for this
Are there any general solutions to this problem? Or how should I actually do using those thinkings above?
P.S. It couldn't be better if some syntax errors like "unclosed quotation mark" can be found.
You need to first define your grammar. This is a simple grammar for your case:
document = *WS [string *WS *(',' *WS string *WS)]
string = %x22 *char %x22
char = %x20-21 / %x23-5B / escape / %x5D-10FFFF
escape = %x5C (%x5C / %x22 / 't' / 'n' / 'r')
WS = %x9 / %x20
You can read it as:
A document may begin/end with a white space, then may have one or more strings separated by commas. Before and after each comma there may be some white space.
A string is made of characters and begins and ends with double quotes Unicode/ASCII hex code 22.
Each character (char), may be: 1) any non control Unicode character before the double quotes i.e. hex 20 (space) or hex 21 (exclamation mark); 2) any character after the double quotes and before the escape slash \ (hex 5C); 3) an escape character sequence; 4) any other Unicode character after the slash (hex 5C).
The escape sequence (rule escape) begins with the escape slash \ and is followed by another slash, or the characters t for tab, n for line feed and r for carriage return. You may add and other escapable characters if you want, as for a C++ string syntax you can see here: https://en.cppreference.com/w/cpp/language/escape .
A white space (WS) is a tab or space, you may add and %xA and %xD for line feed and carriage return respectively.
By the use of this grammar you will get this tree for your input:
The screenshort is from the Tunnel Grammar Studio online laboratory that can run ABNF grammars (as the one above), and I work on.
After you have the grammar, you may use tools to generate a parser, or you can write one yourself. If you want to do it by hand (preferable for so small and simple grammar), you may have one function per each grammar rule that reads one character and checks is it the expected one. If your input finishes when you are parsing the string rule, then you have an input with a started but not finished string.
Your actual string syntax tree will look like that:
I'm having a bit of an issue trying to do an ascii art challenge in GS, since it requires you finishing a line with the \ symbol.
The problem is that "\"p breaks the program since it thinks you escaped a quote, and "\\"p prints two backslashes. I've tried string concatenation, removing one character at a time, printing substrings, etcetc - Nothing seems to work!
I need this string to be printed out, so how would this be done?
It seems that the behavior with p is buggy. I'll look for a place to report it.
However, "\\" by itself does not print two backslashes; it prints one.
Here's a test link to prove it.
Output:
\
"\\" creates a string with 1 backslash because strings are escaped. This is the same as languages like Ruby.
p escapes strings, so a string with one backslash will be displayed as two. This is also the same as languages like Ruby.
So if you want to print a single backslash, or print things without the quotes, you need to print unescaped strings. The best way to do this is with implicit IO (anything on the stack that is left over is printed unescaped).
The program
"\\"
Should print
\
You could also use print or puts if you don't want to use implicit IO.
So I have this string:
{"scores":{"1":["John",60],"2":["Jude",60],"3":["Max",60],"4":["Kyle",60],"5":["Smith",60],"6":["Mark",50],"7":["Luke",40],"8":["Anne",30],"9":["Bruce",20],"10":["kazuo",10]}}
There are a number of integers there that have quotes around them, and I want to get rid of them. How do I do that? I already tried out:
print(string.gsub(string, '/"(\d)"/', "%1"));
but it does not work. :(
Lua does not have regular expressions like Perl, instead, it does have patterns. These are similar with a few differences.
There is no need for delimiting slashes / /, and the escaping character is % but not \. Otherwise, your trial is essentially correct:
print(string.gsub(str, '"(%d+)"', "%1"))
Where str is the variable containing the input string. Also note that string.gsub returns 2 values, which are both printed, the second result being the number of substitutions. Use an extra pair of parentheses to keep only the first result.
You can simplify a little the notation using the colon : operator :
print((str:gsub('"(%d+)"', "%1")))
i need to create a string to store couples of key/value data, for example:
key1::value1||key2::value2||key3::value3
in deserializing it, i may encounter an error if the key or the value happen to contain || or ::
What are common techniques to deal with such situation? thanks
A common way to deal with this is called an escape character or qualifier. Consider this Comma-Separated line:
Name,City,State
John Doe, Jr.,Anytown,CA
Because the name field contains a comma, it of course gets split improperly and so on.
If you enclose each data value by qualifiers, the parser knows when to ignore the delimiter, as in this example:
Name,City,State
"John Doe, Jr.",Anytown,CA
Qualifiers can be optional, used only on data fields that need it. Many implementations will use qualifiers on every field, needed or not.
You may want to implement something similar for your data encoding.
Escape || when serializing, and unescape it when deserializing. A common C-like way to escape is to prepend \. For example:
{ "a:b:c": "foo||bar", "asdf": "\\|||x||||:" }
serialize => "a\:b\:c:foo\|\|bar||asdf:\\\\\|\|\|x\|\|\|\|\:"
Note that \ needs to be escaped (and double escaped due to being placed in a C-style string).
If we assume that you have total control over the input string, then the common way of dealing with this problem is to use an escape character.
Typically, the backslash-\ character is used as an escape to say that "the next character is a special character", so in this case it should not be used as a delimiter. So the parser would see || and :: as delimiters, but would see \|\| as two pipe characters || in either the key or the value.
The next problem is that we have overloaded the backslash. The problem is then, "how do I represent a backslash". This is sovled by saying that the backslash is also escaped, so to represent a \, you would have to say \\. So the parser would see \\ as \.
Note that if you use escape characters, you can use a single character for the delimiters, which might make things simpler.
Alternatively, you may have to restict the input and say that || and :: are just baned and fail/remove when the string is encoded.
A simple solution is to escape a separator (with a backslash, for instance) any time it occurs in data:
Name,City,State
John Doe\, Jr.,Anytown,CA
Of course, the separator will need to be escaped when it occurs in data as well; in this case, a backslash would become \\.
You can use non-ascii character as separator (e.g. vertical tab :-) ).
You can escape separator character in your data during serialization. For example: if you use one character as separator (key1:value1|key2:value2|...) and your data is:
this:is:key1 this|is|data1
this:is:key2 this|is|data2
you double every colon and pipe character in you data when you serialize it. So you will get:
this::is::key1:this||is||data1|this::is::key2:this||is||data2|...
During deserialization whenever you come across two colon or two pipe characters you know that this is not your separator but part of your data and that you have to change it to one character. On the other hand, every single colon or pipe character is you separator.
Use a prefix (say "a") for your special characters (say "b") present in the key and values to store them. This is called escaping.
Then decode the key and values by simply replacing any "ab" sequence with "b". Bear in mind that the prefix is also a special character. An example:
Prefix: \
Special characters: :, |, \
Encoded:
title:Slashdot\: News for Nerds. Stuff that Matters.|shortTitle:\\.
Decoded:
title=Slashdot: News for Nerds. Stuff that Matters.
shortTitle=\.
The common technique is escaping reserved characters, for example:
In urls you escape some characters
using %HEX representation:
http://example.com?aa=a%20b
In programming languages you escape
some characters with a slash prefix:
"\"hello\""