Temperature Charts

I’m trying to make two charts in Google Earth Engine. One of the mean temperature across 20 years, and one of days below 5 C. I’m struggling to resolve the error code “Error generating chart: Data column(s) for axis #0 cannot be of type string”. I’m fairly new to GIS, so I apologize if this is obvious. I’ll include my code below.

I’ve tried rewriting my code from the beginning a few times and I’m exhausted with it.

var states = ee.FeatureCollection("TIGER/2018/States");
var arkansas = states.filter(ee.Filter.eq('NAME', 'Arkansas'));
var temp = ee.ImageCollection("MODIS/061/MOD11A1").select('LST_Day_1km')
  .filterDate('2001-01-01','2021-12-31');
  
var KtoC = temp.map(function(image) {
  return image.multiply(0.02).subtract(273.15);
});

var arkTemp = KtoC.mean().clip(arkansas);

var calculateMonthlyStats = function(imageCollection) {
  var months = ee.List.sequence(1, 12);
  var monthlyStats = months.map(function(month) {
    var start = ee.Date.fromYMD(2001, month, 1);
    var end = start.advance(1, 'month');
    var monthlyData = imageCollection.filterDate(start, end);
    
    // Calculate mean and minimum temperatures
    var meanTemp = monthlyData.mean();
    var minTemp = monthlyData.reduce(ee.Reducer.min());
    
    return ee.Feature(null, {
      'month': ee.Number(month), // Cast month to number
      'meanTemp': meanTemp,
      'minTemp': minTemp
    });
  });
  
  return ee.FeatureCollection(monthlyStats);
};

var monthlyStats = calculateMonthlyStats(temp);

var meanTempChart = ui.Chart.feature.byFeature(monthlyStats, 'month', 'meanTemp')
  .setChartType('ColumnChart')
  .setOptions({
    title: 'Monthly Mean Temperature in Arkansas (2001-2022)',
    hAxis: {title: 'Month'},
    vAxis: {title: 'Temperature (°C)'},
    colors: ['orange']
  });

print(meanTempChart);

var calculateAnnualDaysBelow5C = function(imageCollection) {
  var years = ee.List.sequence(2001, 2022);
  var annualStats = years.map(function(year) {
    var start = ee.Date.fromYMD(year, 1, 1);
    var end = start.advance(1, 'year');
    var yearlyData = imageCollection.filterDate(start, end);

    // Calculate number of days below 5°C
    var daysBelow5C = yearlyData.map(function(image) {
      return image.lt(5).rename('below_5C');
    }).sum();

    return ee.Feature(null, {
      'year': ee.Number(year).format('%d'),
      'daysBelow5C': daysBelow5C
    });
  });
  
  return ee.FeatureCollection(annualStats);
};

var annualDaysBelow5C = calculateAnnualDaysBelow5C(KtoC);

var daysBelow5CChart = ui.Chart.feature.byFeature(annualDaysBelow5C, 'year', 'daysBelow5C')
  .setChartType('ColumnChart')
  .setOptions({
    title: 'Annual Count of Days Below 5°C in Arkansas (2001-2022)',
    hAxis: {title: 'Year'},
    vAxis: {title: 'Count of Days Below 5°C'},
    colors: ['blue']
  });

print(daysBelow5CChart);