formatting arrays with numbers and characters - arrays

Question

I need help turning a Decay.txt file into an array, the first 1-3 and 5th columns are numbers, the third column is "time elapsed" in integers, but the 4th column is a unit of time (milliseconds, Months, Days) but its spelled out with characters. i cant get this mixed array (numbers and characters) to transfer over to matlab
ideally id like to take the unit of time (4th column) change it to a seconds value, (i.e. hour becomes 3600 seconds) then multiply it by the number in the third column and have a final 4 column array where the 3rd column is simply the time elapsed in seconds
anyone know how to do either of these things?
ive tried
Decay = fopen('Decay.txt','r');
B = fscanf(Decay,'%f',[5 inf]);
which stops and has an error as soon as it hits the 4th column
and
Decay = fopen('Decay.txt','r');
B = fscanf(Decay,'%s',[5 inf]);
but this just creates a 5x10000 column where every single number, decimal, and letter is on its own in its own cell of the array

Answer 1

Your first example
Decay = fopen('Decay.txt','r');
B = fscanf(Decay,'%f',[5 inf]);
Breaks because it can't scan the fourth column (a string) as a number (%f). Your second example doesn't have numbers because you're scanning everything as a string (%s).
The correct specifier for your format should be
'%f %f %f %s %f'
However, if you call fscanfwith it, as per documentation:
If formatSpec contains a combination of numeric and character specifiers, then A is numeric, of class double, and fscanf converts each text characters to its numeric equivalent. This occurs even when formatSpec explicitly skips all numeric fields (for example, formatSpec is '%*d %s').
So this input file:
50 1.2 99 s 0
6.42 1.2 3.11 min 1
22 37 0.01 h 2
Has this (undesired) output:
>> fscanf(Decay, "%f %f %f %s %f", [5, inf])
ans =
50.0000 6.4200 110.0000 104.0000
1.2000 1.2000 1.0000 2.0000
99.0000 3.1100 22.0000 0
115.0000 109.0000 37.0000 0
0 105.0000 0.0100 0
That happens because a matrix in MATLAB can't have multiple data of different types. So, your best bet is scanning into a cell array, which can have any type inside.
B = textscan(Decay, "%f %f %f %s %f")
Returns a cell array with the appropriate types. You can use this output to convert the time data into the same unit and build your vectors/matrix. Columns 1, 2, 3 and 5 are trivial to do, just by accessing the cell B{n} for each n.
Column 4 is a cell array of cells. In each internal cell, there's the string you have. You need to apply a conversion from string to the number you need. For my example, such function would look like:
function scale = DecayScale(unit)
switch(unit)
case 's'
scale = 1;
case 'min'
scale = 60;
case 'h'
scale = 3600;
otherwise
throw('Number format not recognized');
end
end
Which you could then apply to the 4th column like:
timeScale = cellfun(#DecayScale, B{4})
And get the final time as:
timeColumn = B{3} .* timeScale