I am trying to create a program that can read out to a csv (comma separated). Is there a way to manipulate say the column width or whether a cell is left or right justified internally from my code so that when i open up the file in excel it looks better than a bunch of strings cramped into tiny cells. My goal is for the user to do as little thinking as possible. If they open up the file and have to size everything right just to see it that seems a little crummy.
CSV is a plain text file format. It doesn't support any visual formatting. For that, you need to write the data to another file format such as .xlsx or .ods.
I have a .CSV file that's storing data from a laser. It records the height of the laser beam every second.
The .CSV file ends up having rows for each measurement that are all in this format:
DR,04,#
where the # is the height reading.
For example, if the beam is at a height of 10, the reading would say:
DR,04,10.
I want my program in C++ to read only the height (third column of the .CSV) from each row and put it into an array. I do not want the first two columns at all. That way I end up with an array with just a bunch of height values from each measurement.
How do I do that?
You can use strtok() to separate out the three columns. And then just get the last value.
You could also just take the string and scan for the first comma, and then scan from there for the second comma. What follows is the value you are after.
You could also use sscanf() to parse out the individual values.
This really isn't a difficult problem, and there are many ways to approach it. That is why people are complaining that you probably should've tried something and then ask a question here when you get stuck on a specific question.
First: I know this would be much easier if it was a .CSV but that is not possible (I'd 'a written the code in the time I wrote this post).
I want to insert numbers given by the user along with a time-stamp into a spreadsheet. There will be a graph in the spreadsheet that automatically generates based on columns a and b, hence the need to not be a .CSV. Column A holds Double-Floats of range 0 through 500 and Column B holds Date and Time information. Inserted rows must be at the top, thus pushing all existing data down by one row, each time.
I've been writing this manually and I think its time to stop doing that. I don't really care what language it is done in, but I would prefer C/C++ using at most the boost libraries. All libraries MUST be open-source. OS is Linux and input should from terminal or at least be given to the program as a parameter, such that the user's input could be piped into the program.
I found this, but I'm not sure if it is the best method as I'm not necessarily locked into python.
Insert row into Excel spreadsheet using openpyxl in Python
Thanks for any and all help.
Have you tried this? A C library that read Excel (xls) files: http://libxls.sourceforge.net.
Hope this meet your need.
An alternative: http://www.libxl.com, more powerful but not open source.
I have two very large lists. They both were originally in excel, but the larger one is a list of emails (about 160,000) of them with other information like their name and address etc. And the smaller one is a list of just 18,000 emails.
My question is what would be the easiest way to get rid of all 18,000 rows from the first document that contain the email addresses from the second?
I was thinking regex or maybe there is another application I can use? I have tried searching online but it seems like there isn't much specific to this. I also tried notepad++ but it freezes when I try to compare these large files.
-Thank You in Advance!!
Good question. One way I would tackle this is making a C++ program [you could extrapolate the idea to the language of your choice; You never mentioned which languages you were proficient in] that read each item of the smaller file into a vector of strings. First, of course, use Excel to save the files as CSV instead of XLS or XLSX, which will comma-separate the values so you can work with them easier. For the larger list, "Save As" a copy of just email addresses, deleting the other rows for now.
Then, you could open the larger list and use a nested loop to check if you should output to an output file. Something like:
bool foundMatch=false;
for(int y=0;y<LargeListVector.size();y++) {
for(int x=0;x<SmallListVector.size();x++) {
if(SmallListVector[x]==LargeListVector[y]) foundMatch=true;
}
if(!foundMatch) OutputVector.append(LargeListVector[y]);
foundMatch=false;
}
That might be partially pseudo-code, but do you get the idea?
So I read a forum post at : Here
=MATCH(B1,$A$1:$A$3,0)>0
Column B would be the large list, with the 160,000 inputs and column A was my list of things I needed to delete of 18,000.
I used this to match everything, and in a separate column pasted this formula. It would print out either an error or TRUE. If the data was in both columns it printed out true.
Then because I suck with excel, I threw this text into Notepad++ and searched for all lines that contained TRUE (match case, because in my case some of the data had the word true in it without caps.) I marked those lines, then under search, bookmarks, I removed all lines with bookmarks. Pasted that back into excel and voila.
I would like to thank you guys for helping and pointing me in the right direction :)
I want to be able to read from an unsorted source text file (one record in each line), and insert the line/record into a destination text file by specifying the line number where it should be inserted.
Where to insert the line/record into the destination file will be determined by comparing the incoming line from the incoming file to the already ordered list in the destination file. (The destination file will start as an empty file and the data will be sorted and inserted into it one line at a time as the program iterates over the incoming file lines.)
Incoming File Example:
1 10/01/2008 line1data
2 11/01/2008 line2data
3 10/15/2008 line3data
Desired Destination File Example:
2 11/01/2008 line2data
3 10/15/2008 line3data
1 10/01/2008 line1data
I could do this by performing the sort in memory via a linked list or similar, but I want to allow this to scale to very large files. (And I am having fun trying to solve this problem as I am a C++ newbie :).)
One of the ways to do this may be to open 2 file streams with fstream (1 in and 1 out, or just 1 in/out stream), but then I run into the difficulty that it's difficult to find and search the file position because it seems to depend on absolute position from the start of the file rather than line numbers :).
I'm sure problems like this have been tackled before, and I would appreciate advice on how to proceed in a manner that is good practice.
I'm using Visual Studio 2008 Pro C++, and I'm just learning C++.
The basic problem is that under common OSs, files are just streams of bytes. There is no concept of lines at the filesystem level. Those semantics have to be added as an additional layer on top of the OS provided facilities. Although I have never used it, I believe that VMS has a record oriented filesystem that would make what you want to do easier. But under Linux or Windows, you can't insert into the middle of a file without rewriting the rest of the file. It is similar to memory: At the highest level, its just a sequence of bytes, and if you want something more complex, like a linked list, it has to be added on top.
If the file is just a plain text file, then I'm afraid the only way to find a particular numbered line is to walk the file counting lines as you go.
The usual 'non-memory' way of doing what you're trying to do is to copy the file from the original to a temporary file, inserting the data at the right point, and then do a rename/replace of the original file.
Obviously, once you've done your insertion, you can copy the rest of the file in one big lump, because you don't care about counting lines any more.
A [distinctly-no-c++] solution would be to use the *nix sort tool, sorting on the second column of data. It might look something like this:
cat <file> | sort -k 2,2 > <file2> ; mv <file2> <file>
It's not exactly in-place, and it fails the request of using C++, but it does work :)
Might even be able to do:
cat <file> | sort -k 2,2 > <file>
I haven't tried that route, though.
* http://www.ss64.com/bash/sort.html - sort man page
One way to do this is not to keep the file sorted, but to use a separate index, using berkley db (BerkleyDB). Each record in the db has the sort keys, and the offset into the main file. The advantage to this is that you can have multiple ways of sorting, without duplicating the text file. You can also change lines without rewriting the file by appending the changed line at the end, and updating the index to ignore the old line and point to the new one. We used this successfully for multi-GB text files that we had to make many small changes to.
Edit: The code I developed to do this is part of a larger package that can be downloaded here. The specific code is in the btree* files under source/IO.
Try a modifed Bucket Sort. Assuming the id values lend themselves well to it, you'll get a much more efficient sorting algorithm. You may be able to enhance I/O efficiency by actually writing out the buckets (use small ones) as you scan, thus potentially reducing the amount of randomized file/io you need. Or not.
Hopefully, there are some good code examples on how to insert a record based on line number into the destination file.
You can't insert contents into a middle of the file (i.e., without overwriting what was previously there); I'm not aware of production-level filesystems that support it.
I think the question is more about implementation rather than specific algorithms, specifically, handling very large datasets.
Suppose the source file has 2^32 lines of data. What would be an efficent way to sort the data.
Here's how I'd do it:
Parse the source file and extract the following information: sort key, offset of line in file, length of line. This information is written to another file. This produces a dataset of fixed size elements that is easy to index, call it the index file.
Use a modified merge sort. Recursively divide the index file until the number of elements to sort has reached some minimum amount - true merge sort recurses to 1 or 0 elements, I suggest stopping at 1024 or something, this will need fine tuning. Load the block of data from the index file into memory and perform a quicksort on it and then write the data back to disk.
Perform the merge on the index file. This is tricky, but can be done like this: load a block of data from each source (1024 entries, say). Merge into a temporary output file and write. When a block is emptied, refill it. When no more source data is found, read the temporary file from the start and overwrite the two parts being merged - they should be adjacent. Obviously, the final merge doesn't need to copy the data (or even create a temporary file). Thinking about this step, it is probably possible to set up a naming convention for the merged index files so that the data doesn't need to overwrite the unmerged data (if you see what I mean).
Read the sorted index file and pull out from the source file the line of data and write to the result file.
It certainly won't be quick with all that file reading and writing, but is should be quite efficient - the real killer is the random seeking of the source file in the final step. Up to that point, the disk access is usually linear and should therefore be reasonably efficient.