Transforming a script into a function with multiple inputs

Hi everyone,

I'm working on a wave dataset stored in a .csv format (I've attached a sample to this post). I'm using the 2019b edition of Matlab. I wrote a script that enables me to plot the changes in wave properties for the chosen month, over the years:

%script to plot changes in wave height data with time
%load data
data=readtable(myfilename);
%create subsets of data divided by month
Jan=data{:,2}==1;
Feb=data{:,2}==2;
%etc...
%define variables
year=Jan{:,1};
height=Jan{:,3};
%plot
figure(1)
clf
plot(year,height,'b')
xlabel('Year')
ylabel('H_s')
hold on
%fit a trendline through the data
height_coeff=polyfit(year,height,1);
height_trend=polyval(height_coeff,year);
plot(year,height_trend,'r');

I would like to turn this into a function with two inputs (filename and month), so that I could change the file and the month of data that I want to plot without editing the code itself. I've tried something like the code below, but it returns an empty graph. I suspect it has something to do with me not defining 'month' correctly, but I don't know how to fix it. Help would be much appreciated

function trial(filename, month)

data=readtable(filename);

Jan=data{:,2}==1;
Feb=data{:,2}==2;
Mar=data{:,2}==3;
Apr=data{:,2}==4;
May=data{:,2}==5;
Jun=data{:,2}==6;
Jul=data{:,2}==7;
Aug=data{:,2}==8;
Sep=data{:,2}==9;
Oct=data{:,2}==10;
Nov=data{:,2}==11;
Dec=data{:,2}==12;

month={Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec};

year=month{:,1};
height=month{:,3};

plot(year,height,'b')
xlabel('Year')
ylabel('H_s')
hold on

height_coeff=polyfit(year,height,1);
height_trend=polyval(height_coeff,year);
plot(year,height_trend,'r');
end

Answer 1

[Sudhakar Shinde]

%load data
myfilename = 'Example.csv';
month = 1;
trial(myfilename, month);

function trial(myfilename, month)
data=readtable(myfilename);
%Extract feb data
[year,height]=Extract(data,month);
plot(year,height,'b')
xlabel('Year')
ylabel('H_s')
hold on
%fit a trendline through the data
height_coeff=polyfit(year,height,1);
height_trend=polyval(height_coeff,year);
plot(year,height_trend,'r');
end


%This function could extract data of jan(1) or feb(2) or march(3).
%Similaraly add cases till dec (12)
function [Year,Height]= Extract(data,month)
switch month
    case 1
        Jan=(data.Month==1);
        Year = data.Year(Jan);
        Height = data.Height(Jan);
    case 2
        FEB=(data.Month==2);
        Year = data.Year(FEB);
        Height = data.Height(FEB);
    case 3
        March=(data.Month==3);
        Year = data.Year(March);
        Height = data.Height(March);
end
end

Answer 2

[Ameer Hamza]

You input variable name is 'month', but you are overwriting it on this line

month={Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec};

Use some other variable name here.