polyfit with cell array with non-uniform dimensions

I have a 10000×1 cell array. This example could clarify my format of data:

Assume 3×1 cell array of this cell array as follow

input_data =

{'[700 900]' }

{'[700 900 1050 800]'}

{'[700]' }

I used this function to convert to double:

Current_mA=cellfun(@str2num,input_data,'UniformOutput',false);

and the output was like this:

{1×2 double}

{1×4 double}

{[ 700]}

or

{[700 900] }

{[700 800 1050 950]}

{[700] }

Voltage_V =

{[3.3 3.4] }

{[2.3 2.37 2.35 2.5]}

{[1.95] }

I want to use below vector to interpolate between data in voltage_V with "polyfit" function

input_current_mA =

750

600

800

approxPoly = polyfit(Current_mA/1000, Voltage_V, size_sample_V - 1);

input_voltage_V = polyval(approxPoly, input_current_mA/1000);

size_sample_V is the number of each data in row. For expample for above Voltage_V:

size_sample_V =

2

4

1

The answer should be:

input_voltage_V =

3.325

2.446

1.95

1. My first question is how to create "size_sample_V" automatically? (size of each row in cell array)
2. If I convert the Current_mA & Voltage_V to array with blanks converted to NaN, how to use "polyfit" function to avoid this answer in output for:

approxPoly =

NaN NaN

3. Can I use cell array to use polyfit?

Thank you in advance for helping.

Answer 1

[KSSV]

Let Current_mA, voltage_V be your cell arrays. They are of equal dimensions.

N = length(approxPoly) ; 
for i = 1:N
    approxPoly{i} = polyfit(Current_mA{i}/1000, Voltage_V{i}, length(Current_mA{i}) - 1);
    input_voltage_V{i} = polyval(approxPoly{i}, input_current_mA{i}/1000);
end

Note that if you have only one data point in the cell array you cannot fit any polynomial.

[Robert]

Thank you.