how to plot data from a cell array that the numbers are type string?

Hi,

I want to plot some lab data. they are collected in txt file, the data itself in txt looks like this

I want to plot the second colum as y and first colum as x

so I use fopen and textscan

fid = fopen('2_nodes_var_coup.txt');
C = textscan(fid,'%s%s');
fclose(fid)
C{1}(1:5,1) %too see some samples
C{2}(1:5,1)

i found that only the format %s will give the data out as string:

ans = 0
ans = 
    {'t i m e '                                   }
    {' S t e p '                                  }
    {' X = 5 0 '                                  }
    {' ( R u n : '                                }
    {' 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 e + 0 0 '}

ans = 
    {' V ( o s c 1 ) '          }
    {' I n f o r m a t i o n : '}
    {' '                        }
    {' 1 / 2 1 ) '              }
    {' 6 . 6 0 0 0 0 4 e - 0 7 '}

if i use %f, then there is error

fid = fopen('2_nodes_var_coup.txt');
C = textscan(fid,'%f%f');
fclose(fid)
C{1}(1:5,1)
C{2}(1:5,1)
ans = 0
Index in position 1 exceeds array bounds.

problem is with the %s method i can't plot

fid = fopen('2_nodes_var_coup.txt');
C = textscan(fid,'%s%s');
fclose(fid)
x= C{1}(5:8,1); %so there are only numbers
y= C{2}(5:8,1);
plot(x,y)

ans = 0
Error using plot
Not enough input arguments.


A = str2double(x)
B = str2double(y)
plot(A,B)
ans = 0
Error using plot
Not enough input arguments.

i don't think i am doing the whole thing right, anyone know what would be the right way to do it?

Thanks!

Answer 1

[Tommy]

Note that str2double for the character vectors you have returns NaN:

>> str2double(' 6 . 6 0 0 0 0 4 e - 0 7 ')

ans =

   NaN

I believe you are ultimately plotting cell arrays filled with NaN:

>> plot({NaN;NaN},{NaN;NaN})
Error using plot
Not enough input arguments.

(Not that the NaNs are causing the error - the cell arrays are:

>> plot({1;2},{1;2})
Error using plot
Not enough input arguments.

But the fact that you're not getting the correct data is another problem.)

I would try to read the file differently. See if this works:

fid = fopen('2_nodes_var_coup.txt');
C = textscan(fid,'%f%f','HeaderLines',2);
fclose(fid)
x= C{1}(5:8,1); %so there are only numbers
y= C{2}(5:8,1);
plot(cell2mat(x),cell2mat(y))

Or how about readtable?

[Xingda Chen]

readtable also works.

it also gave a table which i can change it to a cell array or to a char array. but when i try to use str2double it still gives me NaN, nor it will plot...

[Tommy]

No plot shows, or you get an error? There's a difference.

Why convert to a cell array or char array? If you use

T = readtable('2_nodes_var_coup.txt');

what is contained within T? Why not go directly from there, with something like this:

plot(T.Var1, T.Var2)