function prepareDataForStackedBarChart(data, categories) {
let preparedData = [];
for(let categoryIndex = 0; categoryIndex < categories.length; categoryIndex++) {
let x_vals = [];
let y_vals = [];
for(let index = 0; index < data.length; index++) {
if(data[index].severity_type == categories[categoryIndex] && data[index].smoking_status != 'Unknown') {
x_vals.push(data[index].smoking_status);
y_vals.push(data[index].num_patients);
}
}
let curTrace = {x:x_vals, y:y_vals, name:categories[categoryIndex], type:'bar'};
preparedData.push(curTrace);
}
return preparedData;
}