I am studying mathematical computation and I am completely stuck on this task! I don't even know how to go about starting it!
**Write a program in Fortran that can parse a single line of well-formed HTML or XML markup so that it takes input on a single line (guaranteed to not exceed 80 characters in total) like
-lots of lovely text
where
tag might be anything from 1 to 37 ASCII characters and will not contain spaces
text could contain spaces and be anything from 1 to 73 characters in length
so that the program outputs one of two lines:
tag : text if the two occurrences of tag match inside <...> and
syntax error if anything else is input.
Any help is hugely appreciated !**
There are a number of intrinsic functions for working with strings that may be helpful.
result = index(string, substring) - returns the position of the start of the first occurrence of string substring as a substring in string, counting from one. (Fortran 77)
result = scan(string, set) - scans a string for any of the characters in a set of characters. (Fortran 95)
result = verify(string, set) - verifies that all the characters in a string are present in a set. (Fortran 95)
There are a few user-contributed string tokenization functions on the Fortran Wiki that might be helpful:
delim, strtok, and find_field. Also, FLIBS includes some string manipulation and tokenization routines that might be useful as examples.
Finally, there are a number of existing open-source XML parsers written in Fortran: xmlf90 and xml-fortran. Looking at the source code for these libraries should be helpful.
Related
I'm working with the following code:
Y_Columns <- c("Y.1.1")
paste('{"ImportId":"', Y_Columns, '"}', sep = "")
The paste function produces the following output:
"{\"ImportId\":\"Y.1.1\"}"
How do I get the paste function to omit the \? Such that, the output is:
"{"ImportId":"Y.1.1"}"
Thank you for your help.
Note: I did do a search on SO to see if there were any Q's that asked "what is an escape character in R". But I didn't review all the 160 answers, only the first 20.
This is one way of demonstrating what I wrote in my comment:
out <- paste('{"ImportId":"', Y_Columns, '"}', sep = "")
out
#[1] "{\"ImportId\":\"Y.1.1\"}"
?print
print(out,quote=FALSE)
#[1] {"ImportId":"Y.1.1"}
Both R and regex patterns use escape characters to allow special characters to be displayed in print output or input. (And sometimes regex patterns need to have doubled escapes.) R has a few characters that need to be "escaped" in certain situation. You illustrated one such situation: including double-quote character inside a result that will be printed with surrounding double-quotes. If you were intending to include any single quotes inside a character value that was delimited by single quotes at the time of creation, they would have needed to be escaped as well.
out2 <- '\'quoted\''
nchar(out2)
#[1] 8 ... note that neither the surround single-quotes nor the backslashes get counted
> out2
[1] "'quoted'" ... and the default output quote-char is a double-quote.
Here's a good Q&A to review:How to replace '+' using gsub() function in R
It has two answers, both useful: one shows how to double escape a special character and the other shows how to use teh fixed argument to get around that requirement.
And another potentially useful Q&A on the topic of handling Windows paths:
File path issues in R using Windows ("Hex digits in character string" error)
And some further useful reading suggestions: Look at the series of help pages that start with capital letters. (Since I can never remember which one has which nugget of essential information, I tried ?Syntax first and it has a "See Also" list of essential reading: Arithmetic, Comparison, Control, Extract, Logic, NumericConstants, Paren, Quotes, Reserved. and I then realized what I wanted to refer you to was most likely ?Quotes where all the R-specific escape sequence letters should be listed.
I work with knitr() and I wish to transform inline Latex commands like "\label" and "\ref", depending on the output target (Latex or HTML).
In order to do that, I need to (programmatically) generate valid R strings that correctly represent the backslash: for example "\label" should become "\\label". The goal would be to replace all backslashes in a text fragment with double-backslashes.
but it seems that I cannot even read these strings, let alone process them: if I define:
okstr <- function(str) "do something"
then when I call
okstr("\label")
I directly get an error "unrecognized escape sequence"
(of course, as \l is faultly)
So my question is : does anybody know a way to read strings (in R), without using the escaping mechanism ?
Yes, I know I could do it manually, but that's the point: I need to do it programmatically.
There are many questions that are close to this one, and I have spent some time browsing, but I have found none that yields a workable solution for this.
Best regards.
Inside R code, you need to adhere to R’s syntactic conventions. And since \ in strings is used as an escape character, it needs to form a valid escape sequence (and \l isn’t a valid escape sequence in R).
There is simply no way around this.
But if you are reading the string from elsewhere, e.g. using readLines, scan or any of the other file reading functions, you are already getting the correct string, and no handling is necessary.
Alternatively, if you absolutely want to write LaTeX-like commands in literal strings inside R, just use a different character for \; for instance, +. Just make sure that your function correctly handles it everywhere, and that you keep a way of getting a literal + back. Here’s a suggestion:
okstr("+label{1 ++ 2}")
The implementation of okstr then needs to replace single + by \, and double ++ by + (making the above result in \label{1 + 2}). But consider in which order this needs to happen, and how you’d like to treat more complex cases; for instance, what should the following yield: okstr("1 +++label")?
currently I am working on comparison between SICStus3 and SICStus4 but I got one issue that is SICStus4 will not consult any cases where the comment string has carriage controls or tab characters etc as given below.
Example case as given below.It has 3 arguments with comma delimiter.
case('pr_ua_sfochi',"
Response:
answer(amount(2370.09,usd),[[01AUG06SFO UA CHI Q9.30 1085.58FUA2SFS UA SFO Q9.30 1085.58FUA2SFS NUC2189.76END ROE1.0 XT USD 180.33 ZPSFOCHI 164.23US6.60ZP5.00AY XF4.50SFO4.5]],amount(2189.76,usd),amount(2189.76,usd),amount(180.33,usd),[[fua2sfs,fua2sfs]],amount(6.6,usd),amount(4.5,usd),amount(0.0,usd),amount(18.6,usd),lasttktdate([20061002]),lastdateafterres(200712282]),[[fic_ticketinfo(fare(fua2sfs),fic([]),nvb([]),nva([]),tktiss([]),penalty([]),tktendorsement([]),tourinfo([]),infomsgs([])),fic_ticketinfo(fare(fua2sfs),fic([]),nvb([]),nva([]),tktiss([]),penalty([]),tktendorsement([]),tourinfo([]),infomsgs([]))]],<>,<>,cat35(cat35info([])))
.
02/20/2006 17:05:10 Transaction 35 served by static.static.server1 (usclsefat002:7551) running E*Fare version $Name: build-2006-02-19-1900 $
",price(pnr(
user('atl','1y',<>,<>,dept(<>,'0005300'),<>,<>,<>),
[
passenger(adt,1,[ptconly(n)])
],
[
segment(1,sfo,chi,'ua','<>','100',20140901,0800,f,20140901,2100,'737',res(20140628,1316),hk,pf2(n,[],[],n),<>,flags(no,no,no,no,no,no,no,no,no)),
segment(2,chi,sfo,'ua','<>','101',20140906,1000,f,20140906,1400,'737',res(20140628,1316),hk,pf2(n,[],[],n),<>,flags(no,no,no,no,no,no,no,no,no))
]),[
rebook(n),
ticket(20140301,131659),
dbaccess(20140301,131659),
platingcarrier('ua'),
tax_exempt([]),
trapparm("trap:ffil"),
city(y)
])).
The below predicate will remove comment section in above case.
flatten-cases :-
getmessage(M1),
write_flattened_case(M1),
flatten-cases.
flatten-cases.
write_flattened_case(M1):-
M1 = case(Case,_Comment,Entry),!,
M2 = case(Case,Entry),
writeq(M2),write('.'),nl.
getmessage(M) :-
read(M),
!,
M \== end_of_file.
:- flatten-cases.
Now my requirement is to convert the comment string to an ASCII character list.
Layout characters other than a regular space cannot occur literally in a quoted atom or a double quoted list. This is a requirement of the ISO standard and is fully implemented in SICStus since 3.9.0 invoking SICStus 3 with the option --iso. Since SICStus 4 only ISO syntax is supported.
You need to insert \n and \t accordingly. So instead of
log('Response:
yes'). % BAD!
Now write
log('Response:\n\tyes').
Or, to make it better readable use a continuation escape sequence:
log('Response:\n\
\tyes').
Note that using literal tabs and literal newlines is highly problematic. On a printout you do not see them! Think of 'A \nB' which would not show the trailing spaces nor trailing tabs.
But there are also many other situations like: Making a screenshot of program text, making a photo of program text, using a 3270 terminal emulator and copying the output. In the past, punched cards. The text-mode when reading files (which was originally motivated by punched cards). Similar arguments hold for the tabulator which comes from typewriters with their manually settable tab stops.
And then on SO it is quite difficult to type in a TAB. The browser refuses to type it (very wisely), and if you copy it in, you get it rendered as spaces.
If I am at it, there is also another problem. The name flatten-case should rather be written flatten_case.
I've been using asd=readcsv(filename) to read a csv file in Julia.
The first row of the csv file contains strings which describe the column contents; the rest of the data is a mix of integers and floats. readcsv reads the numbers just fine, but only reads the first 4+1/2 string entries.
After that, it renders "". If I ask the REPL to display asd[1,:], it tells me it is 1x65 Array{Any,2}.
The fifth column in the first row of the csv file (this seems to be the entry it chokes on) is APP #1 bias voltage [V]; but asd[1,5] is just APP . So it looks to me as though readcsv has choked on the "#" character.
I tried using "quotes=false" keyword in readcsv, but it didn't help.
I used to use xlsread in Matlab and it worked fine.
Has anybody out there seen this sort of thing before?
The comment character in Julia is #, and this applies when reading files from delimited text files.
But luckily, the readcsv() and readdlm() functions have an optional argument to help in these situations.
You should try readcsv(filename; comment_char = '/').
Of course, the example above assumes that you don't have any / characters in your first line. If you do, then you'll have to change that / above to something else.
I need to be able to delimit a stream of binary data. I was thinking of using something like the ASCII EOT (End of Transmission) character to do this.
However I'm a bit concerned -- how can I know for sure that the particular binary sequence used for this (0b00000100) won't appear in my own binary sequences, thus giving a false positive on delimitation?
In other words, how is binary delimiting best handled?
EDIT: ...Without using a length header. Sorry guys, should have mentioned this before.
You've got five options:
Use a delimiter character that is unlikely to occur. This runs the risk of you guessing incorrectly. I don't recommend this approach.
Use a delimiter character and an escape sequence to include the delimiter. You may need to double the escape character, depending upon what makes for easier parsing. (Think of the C \0 to include an ASCII NUL in some content.)
Use a delimiter phrase that you can determine does not occur. (Think of the mime message boundaries.)
Prepend a length field of some sort, so you know to read the following N bytes as data. This has the downside of requiring you to know this length before writing the data, which is sometimes difficult or impossible.
Use something far more complicated, like ASN.1, to completely describe all your content for you. (I don't know if I'd actually recommend this unless you can make good use of it -- ASN.1 is awkward to use in the best of circumstances, but it does allow completely unambiguous binary data interpretation.)
Usually, you wrap your binary data in a well known format, for example with a fixed header that describes the subsequent data. If you are trying to find delimeters in an unknown stream of data, usually you need an escape sequence. For example, something like HDLC, where 0x7E is the frame delimeter. Data must be encoded such that if there is 0x7E inside the data, it is replaced with 0x7D followed by an XOR of the original data. 0x7D in the data stream is similarly escaped.
If the binary records can really contain any data, try adding a length before the data instead of a marker after the data. This is sometimes called a prefix length because the length comes before the data.
Otherwise, you'd have to escape the delimiter in the byte stream (and escape the escape sequence).
You can prepend the size of the binary data before it. If you are dealing with streamed data and don't know its size beforehand, you can divide it into chunks and have each chunk begin with size field.
If you set a maximum size for a chunk, you will end up with all but the last chunk the same length which will simplify random access should you require it.
As a space-efficient and fixed-overhead alternative to prepending your data with size fields and escaping the delimiter character, the escapeless encoding can be used to trim off that delimiter character, probably together with other characters that should have special meaning, from your data.
#sarnold's answer is excellent, and here I want to share some code to illustrate it.
First here is a wrong way to do it: using a \n delimiter. Don't do it! the binary data could contain \n, and it would be mixed up with the delimiters:
import os, random
with open('test', 'wb') as f:
for i in range(100): # create 100 binary sequences of random
length = random.randint(2, 100) # length (between 2 and 100)
f.write(os.urandom(length) + b'\n') # separated with the character b"\n"
with open('test', 'rb') as f:
for i, l in enumerate(f):
print(i, l) # oops we get 123 sequences! wrong!
...
121 b"L\xb1\xa6\xf3\x05b\xc9\x1f\x17\x94'\n"
122 b'\xa4\xf6\x9f\xa5\xbc\x91\xbf\x15\xdc}\xca\x90\x8a\xb3\x8c\xe2\x07\x96<\xeft\n'
Now the right way to do it (option #4 in sarnold's answer):
import os, random
with open('test', 'wb') as f:
for i in range(100):
length = random.randint(2, 100)
f.write(length.to_bytes(2, byteorder='little')) # prepend the data with the length of the next data chunk, packed in 2 bytes
f.write(os.urandom(length))
with open('test', 'rb') as f:
i = 0
while True:
l = f.read(2) # read the length of the next chunk
if l == b'': # end of file
break
length = int.from_bytes(l, byteorder='little')
s = f.read(length)
print(i, s)
i += 1
...
98 b"\xfa6\x15CU\x99\xc4\x9f\xbe\x9b\xe6\x1e\x13\x88X\x9a\xb2\xe8\xb7(K'\xf9+X\xc4"
99 b'\xaf\xb4\x98\xe2*HInHp\xd3OxUv\xf7\xa7\x93Qf^\xe1C\x94J)'