Create a logical array based on signal thresholds

How can i create a logical array of zeros and ones based on a threshold (mean +- 3SD) of my signal? I would like to assign a 0 whenever the signal (FxRMS) is above the UpperFxThreshold and below the LowerFxThreshold. When the signal is between these two threshold levels, then i would like to assign a 1. I have plotted the logical array (code below) against my data however, it is incorrect, and i am unsure of how to correct it. I have attached a copy of the script that i have written and example data.

 i
%Create a logical array of force data, where: force above and or below threshold limit = 0, 
%and force between threshold limits = 1
FxLogic = zeros(size(FxRMS));
for iiFx = 500:numel(FxRMS)
    if FxRMS(iiFx)>UpperFxThresh 
        FxLogic(iiFx) = 0;
    elseif FxRMS(iiFx)<LowerFxThresh
        FxLogic(iiFx) = 0;
    else LowerFxThresh<FxRMS(iiFx)<UpperFxThresh
        FxLogic(iiFx) = 1; 
    end
end

Answer 1

[Star Strider]

If I understand correctly what you are doing, and if ‘FxRMS’ is a vector, you can completely eliminate the loop and do your test in one line:

FxLogic = (FxRMS > LowerFxThresh) & (FxRMS < UpperFxThresh);

This sets ‘FxLogic’ to logical 1 or true for ‘FxRMS’ within the limits, and 0 elsewhere. Logical arrays become numeric arrays by doing any operation on them, for example putting a ‘+’ in front of it:

FxLogic = +((FxRMS > LowerFxThresh) & (FxRMS < UpperFxThresh));

producing a double vector.

This should work.

[Cassandra Thompson]

Hi, thank you for your response! This works and is a lot simpler.

The loop i have created does also work, i just realised that there was a mistake in the script elsewhere.

[Star Strider]

As always, my pleasure!

The loop produces the correct result. However with it, ‘FxLogic’ has 499 zeros at the start, because the indexing begins with 500.

[Cassandra Thompson]

FxRMS is medio-lateral ground reaction force (sampled @1000Hz, for 20seconds) during a jump-landing task.

I wanted to ignore any samples prior to ground contact and chose the 500th sample arbitrarily, based on observations of the approximate timing of ground contact between trials, but it's not accurate.

I have created a separate variable to identify the time of ground contact called 'tGND' - and you have just given me the idea to start indexing at the time of ground contact instead.

iiFx = tGND(FxRMS):numel(FxRMS)

So thank you again!

[Star Strider]

As always, my pleasure!