extracting data from hex

Dear all,

I have a .dat file whit hex data. I used 'readtable' to extract the info, but now I want to convert it to decimal using hex2dec. However I had the following error,

Error using hex2num>hex2decImpl (line 57)
Input to hex2num should have just 0-9, a-f, or A-F.

Error in hex2num (line 25)
        x = hex2decImpl(char(s));

The lines I used,

a=readtable('2017-02-10-16-23-46.dat')
a.(3)=hex2num(a.(3)) 

..and a part of the data I'm trying to convert,

    {'0x0000D830'}
    {'0x000103EA'}
    {'0x000105C1'}
    {'0x000079B5'}
    {'0x0000E24D'}
    {'0x0000BB9F'}
    {'0x0000A28F'}

There is any way of remove the 0x000 part? Or any other idea to convert and plot the hex data?

Thanks a lot!

Answer 1

[Guillaume]

Easiest way is to use sscanf instead of hex2dec. sscanf with the '%x' format specifier understand '0x' notation directly:

>> sscanf('0x000103EA', '%x')
ans =
       66538

With your table the simplest way to convert everything would be:

t = readtable('2017-02-10-16-23-46.dat');  %read as table
t = fillmissing(t, 'constant', '0x0', 'DataVariables', @iscellstr);  %replace empty entries by 0x0 for cellstr variables
t = convertvars(t, @iscellstr, @(var) cellfun(@(x) sscanf(x, '%x'), var))  %convert cellstr variables to numbers with sscanf

Note that you may want to store the numbers as uint32 instead of double, in which case that last line becomes:

t = convertvars(t, @iscellstr, @(var) cellfun(@(x) uint32(sscanf(x, '%x'), var)))

One of the major advantage of sscanf over hex2dec is that it can decode 64-bit hexadecimal integers (with the '%lx' format). hex2dec will return rounded results for integers above flintmax:

>> sscanf('0xFFFFFFFFFFFFFFFE', '%lx')  %returns the correct result
ans =
  uint64
   18446744073709551614
   
>> uint64(hex2dec('FFFFFFFFFFFFFFFF')) %returns an incorrect result due to the conversion to double
ans =
  uint64
   18446744073709551615

Answer 2

[Rik]

You should only remove the leading 0x as that indicates the data is hexadecimal.

data_hex={{'0x0000D830'}
    {'0x000103EA'}
    {'0x000105C1'}
    {'0x000079B5'}
    {'0x0000E24D'}
    {'0x0000BB9F'}
    {'0x0000A28F'}};
data_dec=cellfun(@(x) hex2dec(x{1}(3:end)),data_hex);

[Luisa Cencha]

Dear Rik,

Thanks for the answer. I get the following error when trying to use cellfun,

Cell contents reference from a non-cell array object.

However, aa is a cell as far I understood.. Here is the code,

a=readtable('2017-02-10-16-23-46.dat')
aa=table2cell(a)
data_dec=cellfun(@(x) hex2dec(x{1}(3:end)),aa(:,3));

I also tried with aa{:,3} instead and didn't work either. I would really parecciate your help.

[Rik]

I hardly ever work with the table datatype, so can you attach the data file (you'll probably have to zip it). Then I can run your code and make sure the syntax of my code matches your data.

[Luisa Cencha]

Here is the data sample, thank you so much!

[Rik]

You can use Guillaume's suggestion, but the code below works (and fills empty positions with NaN).

a=readtable('2017-02-10-16-23-46.dat');
aa=table2cell(a);
data_dec=cellfun(@parse_fun,aa(:,3:6));

%if you are sure there are no empty cells you don't need parse_fun
%data_dec=cellfun(@(x) hex2dec(x(3:end)),aa(:,3));

function val=parse_fun(str)
if ~isempty(str)
    val=hex2dec(str(3:end));
else
    val=NaN;
end
end

[Guillaume]

Rather than converting to cell, you can work directly on the table with rowfun, varfun or convertvar:

a = convertvar(a, 3:6, @(var) cellfun(@parsefun, var))