I want to create an array in erlang using text editor and run it. But I have no idea how. When I browse it, it's only demonstrated in terminal.
Erlang does not have arrays. Erlang has linked lists, which can be used like arrays but they have there own performance characteristics that make it cheap to access the first item in the list and expensive to access the last item in a large list. You can read more about linked lists here: http://learnyousomeerlang.com/starting-out-for-real#lists
To create a list in a file that file will need to define a module with the same name as the file and export one or more functions. Here is what you might want:
-module(number_list).
-export([base_10/0]).
base_10() ->
[0,1,2,3,4,5,6,7,8,9].
Then compile the file:
erlc number_list.erl
Then use it in the erl shell (assuming you run erl in the same directory as your number_list.beam file):
erl
> number_list:base_10().
[0,1,2,3,4,5,6,7,8,9].
Related
so I'm writing some code that's going to be deployed on a raspberry pi. Because of the computational limitations of the raspberry pi, and the series of steps it's taking for this particular use(image capturing and processing) I thought it would be best to use list comprehension in place of for loops whenever possible. I managed to create a statement that made an array of files(names+paths), if it worked:
self.dark_file_names=np.array([(os.path.join(self.dark_frames_path,
line.strip("\n")) for root, dirs, files in os.walk(self.dark_frames_path) for line in files if line.endswith(".npy\n"))])
however, I tried a variation of this in ipython:
dark_file_names=np.array([(os.path.join(dark_frames_path, line.strip("\n")) for root, dirs, files in os.walk(dark_frames_path) for line in files if line.endswith(".py\n"))])
with this being the output:
array([<generator object <genexpr> at 0x7f14d4412888>], dtype=object)
with dark_frames_path being a local directory with a ton of python files
unfortunately this isn't what I was hoping for. I also tried with a normal list with a similar result. Why is it interpreting my statement as a generator expression instead of a list comprehension?
also I had this working when I was doing it over ssh with these commands in ipython:
stdin, stdout, stderr= ssh.exec_command('ls')
l=[line.strip('\n') for line in stdout if line.strip('\n').endswith(".py")]
with ssh being a paramiko.SSHClient() instance.
How can I create a single simulink file from a simulink model, which consists of mutliple linked blocks in user defined block libraries?
In other words I am looking for a way to break all the library links and have the whole model exist in its own file.
You can do this by saving the file using save_system in the Matlab command window, eg. save_system('mysys','mynewfile.mdl','BreakUserLinks','true'). This will break all your library links and save the whole model in one file.
See also help save_system
How can I create a function with MATLAB so I can call it any where in my code?
I'm new to MATLAB so I will write a PHP example of the code I want to write in MATLAB!
Function newmatlab(n){
n=n+1;
return n;
}
array=array('1','2','3','4');
foreach($array as $x){
$result[]=newmatlab($x);
}
print_f($result);
So in nutshell, I need to loop an array and apply a function to each item in this array.
Can some one show me the above function written in MATLAB so I can understand better?
Note: I need this because I wrote a code that analyzes a video file and then plots data on a graph. I then and save this graph into Excel and jpg. My problem is that I have more than 200 video to analyze, so I need to automate this code to loop inside folders and analyze each *.avi file inside and etc.
As others have said, the documentation covers this pretty thoroughly, but perhaps we can help you understand.
There are a handful of ways that you can define functions in Matlab, but probably the most useful for you to get started is to define one in an m-file. I'll use your example code. You can do this by creating a file called newmatlab.m in your project's directory that looks something like this
% newmatlab.m
function result = newmatlab(array)
result = array + 1
Note that the function has the same name as the file and that there is no explicit return statement - it figures that out by what you've named the output parameter(s) (result in this case).
Then, in the same directory, you can create a script (or another function) that calls your newmatlab function by that name:
% main.m (or whatever)
a = [1 2 3 4];
b = newmatlab(a)
That's it! This is a simplified explanation, but hopefully enough to get you started and then the documentation can help more.
PS: There's no "include" in Matlab; any functions that are defined in m-files in the current path are visible. You can find out what's in the path by using the path command. Roughly, it's going to consist of
Matlab's own directory
The MATLAB subdirectory of your Documents directory
The current working directory
Alright, so, I haven't programmed anything useful in ages - last time I did was a year ago and as you can imagine my knowledge of programming is seriously rusty. (last thing I 'programmed' was a ren'py game over the weekend. One can imagine the limited uses of this. The most advanced C program I wrote was a tic-tac-toe game a year ago. So yeah.)
Anyways, I've been given a job to write a program that takes two Excel files, both of which have a list of items, each associated with an ID. I need to write a program to search both files for IDs and if the IDs match, the program will need to create a new file with the matched IDs and items. This is insanely beyond my limited C capabilities.
If anyone could help, I would seriously appreciate it.
(also, if this is not possible with C, I'll do my best to work with any other languages)
Export the two files to .csv format and write a script to process the two files. For example, in PHP, you have built in csv read/write capabilities.
You can do this with VBA and create a Macro in one of the files which iterates over the cells in your column in file 1 and compares them to cells in file 2 and writes them to a new .xls file if they match.
Dana points out that the VLOOKUP function will do this quite easily.
Install GnuWin32
Output the excel files as text (csv for example)
sort each file with the -u option to remove duplicates if needed
mix and sort the 2 files
count unique IDs with uniq -c
filter out lines with a value of 1 for the count with grep
remove the count leaving the ID and whatever else you need with cut
If you know Java then you can use Apache POI for your project. You can use the examples given on the Apache POI website to accomplish your task.
Apache POI Excel Documentation: http://poi.apache.org/spreadsheet/quick-guide.html
If you absolutely have to do this on xls/xlsx file from a process, you probably need a copy of Excel controlled by COM automation. You can do this in BV/VBA/C#/C++ whatever, some easier than others. Google for 'Excel automation'.
Rgds,
Martin
Not C, but you may be able to cobble something together very quickly using xlsperl.
It has come in handy for me in the past.
just had a general question about how to approach a certain problem I'm facing. I'm fairly new to C so bear with me here. Say I have a folder with 1000+ text files, the files are not named in any kind of numbered order, but they are alphabetical. For my problem I have files of stock data, each file is named after the company's respective ticker. I want to write a program that will open each file, read the data find the historical low and compare it to the current price and calculate the percent change, and then print it. Searching and calculating are not a problem, the problem is getting the program to go through and open each file. The only way I can see to attack this is to create a text file containing all of the ticker symbols, having the program read that into an array and then run a loop that first opens the first filename in the array, perform the calculations, print the output, close the file, then loop back around moving to the second element (the next ticker symbol) in the array. This would be fairly simple to set up (I think) but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this? Not really asking for code ( unless there is some amazing function in c that will do this for me ;) ), just some advice from more experienced C programmers.
Thanks :)
Edit: This is on Linux, sorry I forgot to metion that!
Under Linux/Unix (BSD, OS X, POSIX, etc.) you can use opendir / readdir to go through the directory structure. No need to generate static files that need to be updated, when the file system has the information you want. If you only want a sub-set of stocks at a given time, then using glob would be quicker, there is also scandir.
I don't know what Win32 (Windows / Platform SDK) functions are called, if you are developing using Visual C++ as your C compiler. Searching MSDN Library should help you.
Assuming you're running on linux...
ls /path/to/text/files > names.txt
is exactly what you want.
opendir(); on linux.
http://linux.die.net/man/3/opendir
Exemple :
http://snippets.dzone.com/posts/show/5734
In pseudo code it would look like this, I cannot define the code as I'm not 100% sure if this is the correct approach...
for each directory entry
scan the filename
extract the ticker name from the filename
open the file
read the data
create a record consisting of the filename, data.....
close the file
add the record to a list/array...
> sort the list/array into alphabetical order based on
the ticker name in the filename...
You could vary it slightly if you wish, scan the filenames in the directory entries and sort them first by building a record with the filenames first, then go back to the start of the list/array and open each one individually reading the data and putting it into the record then....
Hope this helps,
best regards,
Tom.
There are no functions in standard C that have any notion of a "directory". You will need to use some kind of platform-specific function to do this. For some examples, take a look at this post from Cprogrammnig.com.
Personally, I prefer using the opendir()/readdir() approach as shown in the second example. It works natively under Linux and also on Windows if you are using Cygwin.
Approach 1) I would just have a specific directory in which I have ONLY these files containing the ticker data and nothing else. I would then use the C readdir API to list all files in the directory and iterate over each one performing the data processing that you require. Which ticker the file applies to is determined only by the filename.
Pros: Easy to code
Cons: It really depends where the files are stored and where they come from.
Approach 2) Change the file format so the ticker files start with a magic code identifying that this is a ticker file, and a string containing the name. As before use readdir to iterate through all files in the folder and open each file, ensure that the magic number is set and read the ticker name from the file, and process the data as before
Pros: More flexible than before. Filename needn't reflect name of ticker
Cons: Harder to code, file format may be fixed.
but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this?
I have solved the exact same problem a while back, albeit for personal uses :)
What I did was to use the OS shell commands to generate a list of those files and redirected the output to a text file and had my program run through them.
On UNIX, there's the handy glob function:
glob_t results;
memset(&results, 0, sizeof(results));
glob("*.txt", 0, NULL, &results);
for (i = 0; i < results.gl_pathc; i++)
printf("%s\n", results.gl_pathv[i]);
globfree(&results);
On Linux or a related system, you could use the fts library. It's designed for traversing file hierarchies: man fts,
or even something as simple as readdir
If on Windows, you can use their Directory Management API's. More specifically, the FindFirstFile function, used with wildcards, in conjunction with FindNextFile