Accomodate for missing values when rendering a portion of a data set with e.g. Google Pie Chart

PartialSetSlicer.cs

/// <summary>
    /// Model to work with a subset of a set and render charts and graphs correctly.
    /// </summary>
    public class PartialSetSlicer
    {
        /// <summary>
        /// Construct a <see cref="PartialSetSlicer" /> with <see cref="Threshold" /> set to the distribution of the last element.
        /// </summary>
        /// <param name="set">Data set.</param>
        /// <param name="size">Size for subset.</param>
        public PartialSetSlicer(
            IEnumerable<AudienceCountryModel> set,
            int size) : this(set, size, 0.05d) => Threshold = (decimal) Countries.Last().Distribution;

        public PartialSetSlicer(
            IEnumerable<AudienceCountryModel> set,
            int size,
            double threshold)
        {
            Countries = set
                        .OrderByDescending(_ => _.Distribution)
                        .ThenBy(_ => _.TwoLetterIsoCountryCode)
                        .Take(size)
                        .ToList();
            Distribution = Countries.Sum(_ => (decimal) _.Distribution);
            if (threshold < 0 && threshold > 1)
            {
                throw new ArgumentException("Threshold must be between 0 and 1", nameof(threshold));
            }

            Threshold = (decimal) threshold;
        }

        public IReadOnlyList<AudienceCountryModel> Countries { get; }

        /// <summary>
        /// Gets the threshold for countries to leave out.
        /// </summary>
        /// <value>
        /// Default is five percent (0.05d)
        /// </value>
        public decimal Threshold { get; }

        /// <summary>
        /// Gets the total distribution for those countries that didn't make it to the top five.
        /// </summary>
        public decimal NotAccountedForDistribution => 1m - Distribution;

        /// <summary>
        /// Gets the distribution for top five countries.
        /// </summary>
        public decimal Distribution { get; }

        public bool HasUnaccountedDistribution => NotAccountedForDistribution != 0;

        /// <summary>
        /// Create dummy rows to batch the not accounted for distribution under the "Other" label
        /// </summary>
        /// <remarks>
        /// Google Charts assume the input is relative, sums to 100%. To show e.g. top five, there is some work to be done to
        /// create a number of dummy rows that are below the threshold value and are unique. This will batch them as "Other"
        /// </remarks>
        /// <returns></returns>
        public IEnumerable<AudienceCountryModel> DummyRows()
        {
            if (!HasUnaccountedDistribution)
            {
                yield break;
            }

            // Calculate new value slightly less than threshold since they will be displayed if equal
            var value = Threshold * 0.99m;
            // Determine how much dummy rows we need to add
            var glitch = NotAccountedForDistribution - Threshold;
            if (glitch < 0)
            {
                // We simply add one row with distribution equal to not accounted for
                yield return new AudienceCountryModel(null, (double) NotAccountedForDistribution);
            }
            else
            {
                // More dummy rows needed. More precisely the divider for not accounted for and threshold
                var multiplier = (int) Math.Round(NotAccountedForDistribution / Threshold);
                // Create dummy rows with unique label
                var query = Enumerable.Range(0, multiplier)
                                      .Select(_ => new AudienceCountryModel(_.ToString(), (double) value));
                // Left overs
                var remainder = NotAccountedForDistribution;
                foreach (var audienceCountryModel in query)
                {
                    remainder -= value;
                    yield return audienceCountryModel;
                }

                if (remainder > 0m)
                {
                    yield return new AudienceCountryModel(multiplier.ToString(), (double) remainder);
                }
            }
        }
    }