I am a novice Go lang programmer,trying to learn Go lang features.I wanted to split a large csv file into multiple files in GO lang, each file containing the header.How do i do this? I have searched everywhere but couldnt get the right solution.Any help in this regard will be greatly appreciated.
Also please suggest me a good book for reference.
Thanking You
Depending on your shell fu this problem might be better suited for common shell utilities but you specifically mentioned go.
Let's think through the problem.
How big is this csv file? Are we talking 100 lines or is it 5G ?
If it's smallish I typically use this:
http://golang.org/pkg/io/ioutil/#ReadFile
However, this package also exists:
http://golang.org/pkg/encoding/csv/
Regardless - let's return to the abstraction of the problem. You have a header (which is the first line) and then the rest of the document.
So what we probably want to do (if ignoring csv for the moment) is to read in our file.
Then we want to split the file body by all the newlines in it.
You can use this to do so:
http://golang.org/pkg/strings/#Split
You didn't mention but do you know how many files you want to split by or would you rather split by the line count or byte count? What's the actual limitation here?
Generally it's not going to be file count but if we pretend it is we simply want to divide our line count by our expected file count to give lines/file.
Now we can take slices of the appropriate size and write the file back out via:
http://golang.org/pkg/io/ioutil/#WriteFile
A trick I use sometime to help think me threw these things is to write down our mission statement.
"I want to split a large csv file into multiple files in go"
Then I start breaking that up into pieces but take the divide/conquer approach - don't try to solve the entire problem in one go - just break it up to where you can think about it.
Also - make gratiutious use of pseudo-code until you can comfortably write the real code itself. Sometimes it helps to just write a short comment inline with how you think the code should flow and then get it down to the smallest portion that you can code and work from there.
By the way - many of the golang.org packages have example links where you can literally run in your browser the example code and cut/paste that to your own local environment.
Also, I know I'll catch some haters with this - but as for books - imo - you are going to learn a lot faster just by trying to get things working rather than reading. Action trumps passivity always. Don't be afraid to fail.
Here is a package that might help. You can set a necessary chunk size in bytes and a file will be split on an appropriate amount of chunks.
Related
I am new to this site and I would like to get some inputs regarding parsing STDF files. Generally speaking, I am trying to parse a STDF file to gather only the results (numbers) and not the rest of the line. If I am able to achieve this, I would then like to compare all the numbers together through a bubble sort or insertion sort and see if any numbers are equal to each other. I am capable of doing this in C/C++ and Java but I have no experience parsing documents using Scripts.
Could anyone push me in the right direction? What should I be reading to learn my way around this?
Are you already using an STDF library?
You did not mention one, so I assume not.
You should find a library you are comfortable with (the list changes over time, but you can find some by Googling or looking at the STDF page on Wikipedia) rather than attempting to parse STDF yourself, unless you have a good reason to recreate the STDF parser wheel.
An STDF file contains many tests. It generally does not make sense to compare the results for different tests, so I assume you are looking for matching values within the set of results for each test.
I would use your chosen STDF parser to read the value of each test for each part. Keep a set of the results for each test. As you read each new result, check the set to see if already exists. If it does, you have found the case you were looking for, otherwise add the result to the set.
I am at the edge of frustration thats why my way of explain myself might be rough.
I am trying to remove a column from a tab delimited text files. I have 10 files with same pattern of names such as (written below), thats why when I use such commands like cut I get frustrated with using tab many times.
So my questions;
1) Is there a easier method of basically copying the file name for overwriting?
cut -f 1,3 oldfile.txt > oldfile.txt
btw when I do the method above, my all lines got erased for some reason.
2) Since I dont know the regular expression well enough, is there a way to go around of awk ? that language seems pretty complicated for me.
3)What is the most memory efficient method for his task? Please tell me a method then I will learn that method even its as hard as learning Chinese.
I am a unix frasturared mediocare. sorry for my bad england.
Best regards,
file name example: KKK12398801_normal_912839.txt
I have a large source code where most of the documentation and source code comments are in english. But one of the minor contributors wrote comments in a different language, spread in various places.
Is there a simple trick that will let me find them ? I imagine first a way to extract all comments from the code and generate a single text file (with possible source file / line number info), then pipe this through some language detection app.
If that matters, I'm on Linux and the current compiler on this project is CLang.
The only thing that comes to mind is to go through all of the code manually and check it yourself. If it's a similar language, that doesn't contain foreign letters, consider using something with a spellchecker. This way, the text that isn't recognized will get underlined, and easy to spot.
Other than that, I don't see an easy way to go through with this.
You could make a program, that reads the files and only prints the comments out to another output file, where you then spell check that file, but this would seem to be a waste of time, as you would easily be able to spot the comments yourself.
If you do make a program for that, however, keep in mind that there are three things to check for:
If comment starts with /*, make sure it stops reading when encountering */
If comment starts with //, only read one line - unless:
If line starting with // ends with \, read next line as well
While it is possible to detect a language from a string automatically, you need way more words than fit in a usual comment to do so.
Solution: Use your own eyes and your own brain...
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
How to read a file from bottom to top in Ruby?
In the course of working on my Ruby program, I had the Eureka Moment that it would be much simpler to write if I were able to parse the text files backwards, rather than forward.
It seems like it would be simple to simply read the text file, line by line, into an array, then write the lines backwards into a text file, parse this temp file forwards (which would now effectively be going backwards) make any necessary changes, re-catalog the resulting lines into an array, and write them backwards a second time, restoring the original direction, before saving the modifications as a new file.
While feasible in theory, I see several problems with it in practice, the biggest of which is that if the size of the text file is very large, a single array will not be able to hold the entirety of the document at once.
Is there a more elegant way to accomplish reading a text file backwards?
If you are not using lots of UTF-8 characters you can use Elif library which work just like File.open. just load Elif and replace File.open with Elif.open
Elif.open('read.txt', "r").each_line{ |s|
puts s
}
This is a great library, but the only problem I am experiencing right now is that it have several problems with line ending in UTF-8. I now have to re-think a way to iterate my files
Additional Details
As I google a way to answer this problem for UTF-8 reverse file reading. I found a way that already implemented by File library:
To read a file backward you can try the ff code:
File.readlines('manga_search.test.txt').reverse_each{ |s|
puts s
}
This can do a good job as well
There's no software limit to Ruby array. There are some memory limitations though: Array size too big - ruby
Your approach would work much faster if you can read everything into memory, operate there and write it back to disk. Assuming the file fits in memory of course.
Let's say your lines are 80 chars wide on average, and you want to read 100 lines. If you want it efficient (as opposed to implemented with the least amount of code), then go back 80*100 bytes from the end (using seek with the "relative to end" option), then read ONE line (this is likely a partial one, so throw it away). Remember your current position via tell, then read everything up until the end.
You now have either more or less than a 100 lines in memory. If less, go back (100+1.5*no_of_missing_lines)*80, and repeat the above steps, but only reading lines until you reach your remembered position from before. Rinse and repeat.
How about just going to the end of the file and iterating backwards over each char until you reach a newline, read the line, and so on? Not elegant, but certainly effective.
Example: https://gist.github.com/1117141
I can't think of an elegant way to do something so unusual as this, but you could probably do it using the file-tail library. It uses random access files in Ruby to read it backwards (and you could even do it yourself, look for random access at this link).
You could go throughout the file once forward, storing only the byte offset of each \n instead of storing the full string for each line. Then you traverse your offset array backward and can use ios.sysseek and ios.sysread to get lines out of the file. Unless your file is truly enormous, that should alleviate the memory issue.
Admitedly, this absolutely fails the elegance test.
Sadly, a project that I have been working on lately has a large amount of copy-and-paste code, even within single files. Are there any tools or techniques that can detect duplication or near-duplication within a single file? I have Beyond Compare 3 and it works well for comparing separate files, but I am at a loss for comparing single files.
Thanks in advance.
Edit:
Thanks for all the great tools! I'll definitely check them out.
This project is an ASP.NET/C# project, but I work with a variety of languages including Java; I'm interested in what tools are best (for any language) to remove duplication.
Check out Atomiq. It finds code that is duplicate that is prime for extracting to one location.
http://www.getatomiq.com/
If you're using Eclipse, you can use the copy paste detector (CPD) https://olex.openlogic.com/packages/cpd.
You don't say what language you are using, which is going to affect what tools you can use.
For Python there is CloneDigger. It also supports Java but I have not tried that. It can find code duplication both with a single file and between files, and gives you the result as a diff-like report in HTML.
See SD CloneDR, a tool for detecting copy-paste-edit code within and across multiple files. It detects exact copyies, copies that have been reformatted, and near-miss copies with different identifiers, literals, and even different seqeunces of statements.
The CloneDR handles many languages, including Java (1.4,1.5,1.6) and C# especially up to C#4.0. You can see sample clone detection reports at the website, also including one for C#.
Resharper does this automagically - it suggests when it thinks code should be extracted into a method, and will do the extraction for you
Check out PMD , once you have configured it (which is tad simple) you can run its copy paste detector to find duplicate code.
One with some Office skills can do following sequence in 1 minute:
use ordinary formatter to unify the code style, preferably without line wrapping
feed the code text into Microsoft Excel as a single column
search and replace all dual spaces with single one and do other replacements
sort column
At this point the keywords for duplicates will be already well detected. But to go further
add comparator formula to 2nd column and counter to 3rd
copy and paste values again, sort and see the most repetitive lines
There is an analysis tool, called Simian, which I haven't yet tried. Supposedly it can be run on any kind of text and point out duplicated items. It can be used via a command line interface.
Another option similar to those above, but with a different tool chain: https://www.npmjs.com/package/jscpd