Matlab Text file I/o

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Priyamvada Shankar
Priyamvada Shankar 2019-3-24
评论： Walter Roberson 2021-3-30
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
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Paul Braverman
Paul Braverman 2020-2-1
They key is to use the fileread function
function charnum = char_counter(fname,character)
if ischar(character)==0 | fopen(fname)==-1
charnum=-1
else
A=double(char(fileread(fname)))';
charnum=sum(A==double(character));
end
end
Walter Roberson
Walter Roberson 2020-2-1
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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回答（6 个）

Kumar Vivek
Kumar Vivek 2020-5-14
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
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Farhaan Zaidi Bhat
Farhaan Zaidi Bhat 2020-12-14
Can someone tell me what affect did the return statement have?
Walter Roberson
Walter Roberson 2020-12-14
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 2019-3-24
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?
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paul mary
paul mary 2019-3-24
@Walter Roberson, Thank you so much, you gave me the best tip.
So Priyamvada, I can give you some hints.
  1. does the file exist? think about function exist() in matlab documentation
  2. think about count() function
  3. Using fread() function is the right thing to do.
asad jaffar
asad jaffar 2019-4-20
@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 2020-3-18
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
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sri harsha juttiga
sri harsha juttiga 2020-4-5
function charnum=char_counter(fname,character)
fid = fopen(fname, 'rt');
if fid<0 || ischar(character)==0
%error('error opening file %s\n\n', fname);
charnum=-1; %for not valid chars or files
return
end
online = fgets(fid); n=0; % this loop is for checking line by line.
while ischar(online)
for ii=1:length(online)
p=online(ii);
if ischar(p)
if (p == character)
n=n+1;
end
end
end
online=fgets(fid);
end
if n==0
charnum=0;
else charnum=n; end
fclose(fid);
Walter Roberson
Walter Roberson 2020-4-6
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 2020-7-16
编辑：Kumar Shubham 2020-7-16
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.
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Chandan Kumar
Chandan Kumar 2021-3-18
function charnum = char_counter(filename,character)
fid = fopen(filename,'rt');
charnum=0;
if ~ischar(character) || length(character)~=1 || fid<0
charnum=-1;
return;
end
oneline=fgets(fid);
while ischar(tline)
matches=strfind(tline,character);
num=length(matches);
charnum=charnum+num;
oneline=fgets(fid);
end
fclose(fid);
Walter Roberson
Walter Roberson 2021-3-18
@Chandan Kumar
You do not always close the file that you succeed in opening.

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Sravani Kurma
Sravani Kurma 2020-7-28
编辑：Sravani Kurma 2020-7-28
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)
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Sravani Kurma
Sravani Kurma 2020-7-28
编辑：Sravani Kurma 2020-7-28
MATLAB has reserved values of fid like fid==0 for std input ,
fid ==1 for std o/p,
fid ==2 for std error.
As the given file is for binary read access,i can take f>2 or f~=0(since no reserved values are possibily found).
Ya fclose has to be done .... I will edit that
Walter Roberson
Walter Roberson 2020-8-6
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 2021-3-29
编辑：Ahmed Saleh 2021-3-29
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 个评论
Walter Roberson
Walter Roberson 2021-3-30
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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