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Matlab Text file I/o

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Priyamvada Shankar
Priyamvada Shankar on 24 Mar 2019
Commented: Walter Roberson on 30 Mar 2021
Write a function called char_counter that counts the number of a certain character in a text file. The function takes two input arguments, fname, a char vector of the filename and character, the char it counts in the file. The function returns charnum, the number of characters found. If the file is not found or character is not a valid char, the function return -1. As an example, consider the following run. The file "simple.txt" contains a single line: "This file should have exactly three a-s..." charnum = char_counter('simple.txt','a') charnum = 3
  4 Comments
Walter Roberson
Walter Roberson on 1 Feb 2020
You leak open files. You open the file but do not close it. MATLAB does not automatically close files when you return from a function.

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Answers (6)

Kumar Vivek
Kumar Vivek on 14 May 2020
function charnum = char_counter(fname,character)
fid = fopen(fname,'rt');
if (fid<0) || ~ischar(character)
charnum = -1;
return;
end
oneline = fgets(fid);
charnum = 0;
while (ischar(oneline)) || (strcmp(character,oneline)==1)
f = strfind(oneline,character);
charnum = charnum + length(f);
oneline = fgets(fid);
end
end
  5 Comments
Walter Roberson
Walter Roberson on 14 Dec 2020
return causes matlab to leave the function. The values that will be returned to the caller will be according to whatever has been assigned at that point in the execution. In this particular case, the caller would receive the value -1 .
Because the function has been left, the code would not continue on to
oneline = fgets(fid);
You would be in trouble if you did continue on to that point, as the case of fid<0 corresponds to a failure to open the file, and if the file could not be opened there is no way you can read from the file.
Another equivalent way of writing the code would be
function charnum = char_counter(fname,character)
fid = fopen(fname,'rt');
if (fid<0) || ~ischar(character)
charnum = -1;
else
oneline = fgets(fid);
charnum = 0;
while (ischar(oneline)) || (strcmp(character,oneline)==1)
f = strfind(oneline,character);
charnum = charnum + length(f);
oneline = fgets(fid);
end
end
end
However, situations in which return() tend to get used can be more difficult to convert than this, such as if you are inside a loop.

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Kodavati Mahendra
Kodavati Mahendra on 24 Mar 2019
charnum = char_counter('simple.txt','a')
function charnum = char_counter(a,b);
f = fopen(a);
c = textscan(f,'%s');
charnum = sum(sum(char(c{:})==b));
end
Something lilke this?
  13 Comments
asad jaffar
asad jaffar on 20 Apr 2019
@priyamvada shanker ,can you kindly guide me ? i am using the same code of yours but it is giving error ,can someone here give me few hints or tell me about the alogrithm.

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sadek kouz
sadek kouz on 18 Mar 2020
i tried this but i still got an error for
Assessment result: incorrectTest with all visible characters
Variable charnum has an incorrect value. When testing with ' ' your solution returned 2 which is incorrect. (75444)
function charnum = char_counter(filename,character)
charnum=0;
if ~ischar(character)
charnum=-1;
return;
end
if length(character)~=1
charnum=-1;
return;
end
fid = fopen(filename,'rt');
if fid<0
charnum=-1;
return;
end
oneline= fgets(fid);
while ischar(oneline)
a=sprintf('%s \n',oneline);
c=strfind(a,character);
charnum=length(c);
oneline=fgets(fid);
end
end
  3 Comments
Walter Roberson
Walter Roberson on 6 Apr 2020
If the file name is valid but the second entry is not character type, then the fopen will succeed but the ischar() test will fail, leading you to return, without having fclose() after the successful fopen.
while ischar(online)
In order for that to succeed, online must be character data type. In MATLAB, if an array is a particular data type, every element of the array is also that data type. (In some cases involving handle mixins, the elements of the array might also satisfy more restrictive data types as well.)
p=online(ii);
In order to get here, online must have been character data type. When it is, each element extracted from it must also be character data type.
if ischar(p)
You could not have reached this statement if p was not a char, so there is no point doing this test.

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Kumar Shubham
Kumar Shubham on 16 Jul 2020
Edited: Kumar Shubham on 16 Jul 2020
after hours i was able to come up with the code that passes test cases.
function charnum = char_counter(filename,character)
%deals with all negations
fid = fopen(filename,'rt');
charnum=0;
if ~ischar(character) || length(character)~=1 || fid<0
charnum=-1;
return;
end
%the concerned code for test case 1 and 2
tline=fgetl(fid);
while ischar(tline)
matches=strfind(tline,character);
num=length(matches);
if num>0
charnum=charnum+num;
end
tline=fgetl(fid);
end
above is more like a combiantion of different ideas from various answers, i suppose there is room for efficiency, please give your input.
  3 Comments
Walter Roberson
Walter Roberson on 18 Mar 2021
You do not always close the file that you succeed in opening.

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Sravani Kurma
Sravani Kurma on 28 Jul 2020
Edited: Sravani Kurma on 28 Jul 2020
function charnum=char_counter(fname,character)
fid=fopen(fname,'rt');
if fid<0 % for invalid file,return -1
charnum= -1;
return
end
count=0;
if fid ~=0 && ischar(character)==true
oneline=fgets(fid); %copy file text to oneline
while ischar(oneline) % to check line by line
for i=1:1:length(oneline) % each and every character of oneline is compared with the given input charcter
if oneline(i)==character % if characters matched,count increment
count=count+1;
end
end
oneline=fgets(fid);% update nextline
end
charnum=count; %final count stored in charnum
else
charnum=-1;
end
fclose(fid)
  3 Comments
Walter Roberson
Walter Roberson on 6 Aug 2020
Yes, MATLAB has those reserved file identifiers, but
fid=fopen(fname,'rt');
will never return 0, 1, or 2, so there is no point in testing for the possibility.

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Ahmed Saleh
Ahmed Saleh on 29 Mar 2021
Edited: Ahmed Saleh on 29 Mar 2021
function charnum = char_counter(fname,character)
if ~ischar(fname) || character <32 || character >126
charnum=-1;
return
end
fid=fopen(fname,'rt');
if fid <0 || nargin<2
charnum=-1;
return
end
text = fgets(fid);
char=[];
while ischar(text)
char=[char,text];
text = fgets(fid);
end
s=size(char);
count=0;
for ii=1:s(2)
logic=strcmp(character,char(1,ii));
if logic==1
count=count+1;
end
end
charnum=count;
  1 Comment
Walter Roberson
Walter Roberson on 30 Mar 2021
If nargin < 2 then character will not be defined for the test in your first if , so it does not make sense to test nargin < 2 after that if test.
Character positions less than 32 are valid characters -- especially 10 (newline) and 13 (carriage return)
However, if the user passes a number in as the second parameter, then that would not be a valid character. And if you thought that the character was being passed in as a number, you failed to check for possibilities such as 98.6

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