cell array to numeric array for plotting

Question

I have a cell array containing historic gold price data and a cell array with the associated dates. I want to plot dates against prices for simple analysis but I am having difficulty converting the cell array of prices into a doubles.

My code is:

figure
plot(Date,USDAM,'b')
title('{\bf US Gold Daily Market Price, 2010 to 2015}')
datetick
axis tight

When I try to convert the gold prices (USDAM) into a double using cell2mat(USDAM), it throws the following error:

Error using cat Dimensions of matrices being concatenated are not consistent.

Error in cell2mat (line 83) m{n} = cat(1,c{:,n});

I use the following code to import the data:

filename = 'goldPriceData.csv';
delimiter = ',';
startRow = 2;
endRow = 759;
formatSpec = '%s%s%*s%*s%*s%*s%*s%[^\n\r]';

fileID = fopen(filename,'r');


dataArray = textscan(fileID, formatSpec, endRow-startRow+1, 'Delimiter', delimiter, 'EmptyValue' ,NaN,'HeaderLines', startRow-1, 'ReturnOnError', false);

fclose(fileID);

Date = dataArray{:, 1};
USDAM = dataArray{:, 2};

Answer 1

For your problem, cell2mat is the wrong function. Consider the cell array of strings:

>> S = {'1.2';'3.14159';'2.718'}
S = 
    '1.2'
    '3.14159'
    '2.718'
>> cell2mat(S)
Error using cat
Dimensions of matrices being concatenated are not consistent.
Error in cell2mat (line 83)
            m{n} = cat(1,c{:,n}); 

That's because each row of the output needs to have the same number of columns, the strings are of different length. You can use strvcat(S) to get a rectangular matrix padded with spaces, but that isn't what you want. You want numeric data.

>> str2double(S)
ans =
    1.2000
    3.1416
    2.7180

Just because it puts a number in scientific notation, doesn't mean it's not the same number. That is, 1.199250000000000e+03 is 1199.25. To get the tick labels looking the way you want them, set YTickLabel property of the axis with formatted strings, the ones in USD.

Regarding your dates, you'll need numeric data to plot on each axis so convert the dates with datenum.

>> dateVals = datenum({'2014-12-30', '2014-12-31'})
dateVals =
      735963
      735964

Then to get the dates displayed on the x axis correctly, set the XTickLabel properties of the axis to get it looking how you want it (using the strings in Dates). Note that for setting the tick labels, you must ensure that you have the correct (same) number of ticks as labels that you indent to have. But that is a different question, I think.