I have the following array:-
dir=['E','B','R']
I want to find the index of the elemen 'E'.
>> find(dir=='E')
ans =
1
But i want to do the same for an array of strings rather than array of characters like:
dir=['E','G','T','BR']
But there is an error to find 'BR'. I want the output to be 4.
>> find(dir=='BR')
Error using ==
Matrix dimensions must agree.
How to work-around this error?
I recommend you look at the documentation on string (char array) handling in matlab such as here.
What you want to do is work with cell arrays of strings:
dir = {'E','G','T','BR'}
find(ismember(dir,'BR'))
ans = 4
Related
How can I iterate over a string in Python (get each character from the string, one at a time, each time through a loop)?
As Johannes pointed out,
for c in "string":
#do something with c
You can iterate pretty much anything in python using the for loop construct,
for example, open("file.txt") returns a file object (and opens the file), iterating over it iterates over lines in that file
with open(filename) as f:
for line in f:
# do something with line
If that seems like magic, well it kinda is, but the idea behind it is really simple.
There's a simple iterator protocol that can be applied to any kind of object to make the for loop work on it.
Simply implement an iterator that defines a next() method, and implement an __iter__ method on a class to make it iterable. (the __iter__ of course, should return an iterator object, that is, an object that defines next())
See official documentation
If you need access to the index as you iterate through the string, use enumerate():
>>> for i, c in enumerate('test'):
... print i, c
...
0 t
1 e
2 s
3 t
Even easier:
for c in "test":
print c
Just to make a more comprehensive answer, the C way of iterating over a string can apply in Python, if you really wanna force a square peg into a round hole.
i = 0
while i < len(str):
print str[i]
i += 1
But then again, why do that when strings are inherently iterable?
for i in str:
print i
Well you can also do something interesting like this and do your job by using for loop
#suppose you have variable name
name = "Mr.Suryaa"
for index in range ( len ( name ) ):
print ( name[index] ) #just like c and c++
Answer is
M r . S u r y a a
However since range() create a list of the values which is sequence thus you can directly use the name
for e in name:
print(e)
This also produces the same result and also looks better and works with any sequence like list, tuple, and dictionary.
We have used tow Built in Functions ( BIFs in Python Community )
1) range() - range() BIF is used to create indexes
Example
for i in range ( 5 ) :
can produce 0 , 1 , 2 , 3 , 4
2) len() - len() BIF is used to find out the length of given string
If you would like to use a more functional approach to iterating over a string (perhaps to transform it somehow), you can split the string into characters, apply a function to each one, then join the resulting list of characters back into a string.
A string is inherently a list of characters, hence 'map' will iterate over the string - as second argument - applying the function - the first argument - to each one.
For example, here I use a simple lambda approach since all I want to do is a trivial modification to the character: here, to increment each character value:
>>> ''.join(map(lambda x: chr(ord(x)+1), "HAL"))
'IBM'
or more generally:
>>> ''.join(map(my_function, my_string))
where my_function takes a char value and returns a char value.
Several answers here use range. xrange is generally better as it returns a generator, rather than a fully-instantiated list. Where memory and or iterables of widely-varying lengths can be an issue, xrange is superior.
You can also do the following:
txt = "Hello World!"
print (*txt, sep='\n')
This does not use loops but internally print statement takes care of it.
* unpacks the string into a list and sends it to the print statement
sep='\n' will ensure that the next char is printed on a new line
The output will be:
H
e
l
l
o
W
o
r
l
d
!
If you do need a loop statement, then as others have mentioned, you can use a for loop like this:
for x in txt: print (x)
If you ever run in a situation where you need to get the next char of the word using __next__(), remember to create a string_iterator and iterate over it and not the original string (it does not have the __next__() method)
In this example, when I find a char = [ I keep looking into the next word while I don't find ], so I need to use __next__
here a for loop over the string wouldn't help
myString = "'string' 4 '['RP0', 'LC0']' '[3, 4]' '[3, '4']'"
processedInput = ""
word_iterator = myString.__iter__()
for idx, char in enumerate(word_iterator):
if char == "'":
continue
processedInput+=char
if char == '[':
next_char=word_iterator.__next__()
while(next_char != "]"):
processedInput+=next_char
next_char=word_iterator.__next__()
else:
processedInput+=next_char
I am trying to read an excel sheet and then and find cells that are not empty and have date information in them by finding two '/' in a string
but matlab keeps to erroring on handling cell type
"Undefined operator '~=' for input arguments of type 'cell'."
"Undefined function 'string' for input arguments of type 'cell'."
"Undefined function 'char' for input arguments of type 'cell'."
MyFolderInfo = dir('C:\');
filename = 'Export.xls';
[num,txt,raw] = xlsread(filename,'A1:G200');
for i = 1:length(txt)
if ~isnan(raw(i,1))
if sum(ismember(char(raw(i,1)),'/')) == 2
A(i,1) = raw(i,1);
end
end
end
please help fixing it
There are multiple issues with your code. Since raw is a cell array, you can't run isnan on it, isnan is for numerical arrays. Since all you're interested in is cells with text in them, you don't need to use raw at all, any blank cells will not be present in txt.
My approach is to create a logical array, has_2_slashes, and then use it to extract the elements from raw that have two slashes in them.
Here is my code. I generalized it to read multiple columns since your original code only seemed to be written to handle one column.
filename = 'Export.xls';
[~, ~, raw] = xlsread(filename, 'A1:G200');
[num_rows, num_cols] = size(raw);
has_2_slashes = false(num_rows, num_cols);
for row = 1:num_rows
for col = 1:num_cols
has_2_slashes(row, col) = sum(ismember(raw{row, col}, '/')) == 2;
end
end
A = raw(has_2_slashes);
cellfun(#numel,strfind(txt,'/'))
should give you a numerical array where the (i,j)th element contains the number of slashes. For example,
>> cellfun(#numel,strfind({'a','b';'/','/abc/'},'/'))
ans =
0 0
1 2
The key here is to use strfind.
Now you may want to expand a bit in your question on what you intend to do next with txt -- in other words, specify desired output more, which is always a good thing to do. If you intend to read the dates, it may be better to just read it upfront, for example by using regexp or datetime as opposed to getting an array which can then map to where the dates are. As is, using ans>=2 next gives you the logical array that can let you extract the matched entries.
I have a few lines of text like this:
abc
def
ghi
and I want to assign these multiple lines to a Matlab variable for further processing.
I am copying these from very large text file and want to process it in Matlab Instead of saving the text into a file and then reading line by line for processing.
I tried to handle the above text lines as single string but am getting an error whilst trying to assign to a variable:
x = 'abc
def
ghi'
Error:
x = 'abc
|
Error: String is not terminated properly.
Any suggestions which could help me understand and solve the issue will be highly appreciated.
I frequently do this, namely copy text from elsewhere which I want to hard-code into a MATLAB script (in my case it's generally SQL code I want to manipulate and call from MATLAB).
To achieve this I have a helper function in clipboard2cellstr.m defined as follows:
function clipboard2cellstr
str = clipboard('paste');
str = regexprep(str, '''', ''''''); % Double any single quotes
strs = regexp(str, '\s*\r?\n\r?', 'split');
cs = sprintf('{\n''%s''\n}', strjoin(strs, sprintf('''\n''')));
clipboard('copy', cs);
disp(cs)
disp('(Copied to Clipboard)')
end
I then copy the text using Ctrl-c (or however) and run clipboard2cellstr. This changes the contents of the clipboard to something I can paste into the MATLAB editor using Ctrl-v (or however).
For example, copying this line
and this line
and this one, and then running the function generates this:
{
'For example, copying this line'
'and this line'
'and this one, and then running the function generates this:'
}
which is valid MATLAB which can be pasted directly in.
Your error is because you ended the line when MATLAB was expecting a closing quote character. You must use array notation to have multi-line or multi-element arrays.
You can assign like this if you use array notation
x = ['abc'
'def'
'hij']
>> x = 3×3 char array
Note: with this method, your rows must have the same number of characters, as you are really dealing with a character array. You can think of a character array like a numeric matrix, hence why it must be "rectangular".
If you have MATLAB R2016b or newer, you can use the string data type. This uses double quotes "..." rather than single quotes '...', and can be multi-line. You must still use array notation:
x = ["abc"
"def"
"hijk"]
>> x = 3×1 string array
We can have different numbers of characters in each line, as this is simply a 3 element string array, not a character array.
Alternatively, use a cell array of character arrays (or strings)
x = {'abc'
'def'
'hijk'}
>> x = 3×1 cell array
Again, you can have character arrays or strings of different lengths within a cell array.
In all of the above examples, a newline is simply for readability and can be replaced by a semi-colon ; to denote the next line of the array.
The option you choose will depend on what you want to do with the text. If you're reading from a file, I would suggest the string array or the cell array, as they can deal with different length lines. For backwards compatibility, use a cell array. You may find cellfun relevant for operating on cell arrays. For native string operations, use a string array.
I am trying to read a tag from XML and then want to concatenate a number to it.
Firstly, I am saving the value of the string to a variable and trying to concatenate it
with the variable in the for loop. But it throws an error.
for i = 0:tag.getLength-1
node = tag.item(i);
disp([node.getTextContent]);
str=node.getTextContent;
str= strcat(str, num2str(i))
new_loads = cat(2,loads,[node.getTextContent]);
end
Error thrown is
Operands to the || and && operators must be
convertible to logical scalar values.
Error in strcat (line 83)
if ~isempty(str) && (str(end) == 0 ||
isspace(str(end)))
Error in SMERCGUI>pushbutton1_Callback (line 182)
str= strcat(str,' morning')
Error in gui_mainfcn (line 96)
feval(varargin{:});
Error in SMERCGUI (line 44)
gui_mainfcn(gui_State, varargin{:});
Error in
#(hObject,eventdata)SMERCGUI('pushbutton1_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating uicontrol Callback
The error suggests that your string is not a string. It's not clear to me whether it's throwing an error at the strcat line, or at the later cat line.
At any rate, it should be clear that you cannot concatenate elements of different types into an array - cell array yes, regular array no. So the line
new_loads = cat(2,loads,[node.getTextContent]);
is bound to give a problem. 2 is numerical, and node.getTextContent is a string - or maybe a cell array or something else. I can't see what loads is, so I can't tell if that is involved in the problem.
Usually a good way to combine numbers and strings into a single string is
newString = sprintf('%s %d', oldString, number);
You can then use all the formatting tricks of printf to produce output exactly as you want. But before you do anything, make sure you understand the type of all the elements you are trying to string together. The easiest way to do this for all the elements in memory is
whos
Or if you just want it for one variable,
whos str
Or all variables starting with s:
whos s*
The output is self-explanatory. If you still can't figure it out after this, leave a comment and I'll try to help you out.
EDIT based on what I read at http://blogs.mathworks.com/community/2010/11/01/xml-and-matlab-navigating-a-tree/ , it is possible that you just need to cast your str variable to a Matlab string (apparently it's a java.lang.string). So try to add
str = char(str);
before using str. It may be what you need.
I would like to make a list of strings in MATLAB using the example below:
x = ['fun', 'today', 'sunny']
I want to be able to call x(1) and have it return 'fun', but instead I keep getting 'f'.
Also, is there a way to add a string to a list without getting the list giving back a number where the string should be? I have tried using str2double and a few other things. It seems like both of these thing should be possible to do in MATLAB.
The easiest way to store a list of strings that have different lengths is to use cell arrays. For example:
>> x = {'fun', 'today', 'sunny'}; %# Create a cell array of strings
>> x{1} %# Get the string from the first cell
ans =
fun
It's kind of a kludgy workaround, but
x = strsplit('fun.today.sunny', ',')
produces a list with individual, callable strings.