Python-compute the histogram of a set of data

Question

The Python function below is to compute histogram of data, with equal-sized bins. I would like to get the correct result

[1, 6, 4, 6]

However after I run the code, it get result

[7, 12, 17, 17]

which is not correct. Can anybody know how to fix it?

# Computes the histogram of a set of data

def histogram(data, num_bins):



# Find what range the data spans, and use it to calculate the bin size.

span = max(data) - min(data)

bin_size = span / num_bins



# Calculate the thresholds for each bin.

thresholds = [0] * num_bins

for i in range(num_bins):

    thresholds[i] += bin_size * (i+1)



# Compute the histogram

counts = [0] * num_bins

for datum in data:

    # Increment the count of the bin that the datum falls in

    for bin_index, threshold in enumerate(thresholds):

        if datum <= threshold:

            counts[bin_index] += 1

return counts



# Some random data

data = [-3.2, 0, 1, 1.5, 1.6, 1.9, 5, 6, 9, 1, 4, 5, 8, 9, 5, 6.7, 9]

print("Correct result:\t" + str([1, 6, 4, 6]))

print("Your result:\t" + str(histogram(data, num_bins=4)))

Answer 1

Only you have two logical errors

(1) calculating the threshold

(2) add break in for, once found the range

def histogram(data, num_bins):
  span = max(data) - min(data)
  bin_size = float(span) / num_bins
  thresholds = [0] * num_bins

  for i in range(num_bins):
    #I change thresholds calc
    thresholds[i] = min(data) + bin_size * (i+1)

  counts = [0] * num_bins
  for datum in data:
    for bin_index, threshold in enumerate(thresholds):
      if datum <= threshold:
        counts[bin_index] += 1
        #I add a break
        break
  return counts

data = [-3.2, 0, 1, 1.5, 1.6, 1.9, 5, 6, 9, 1, 4, 5, 8, 9, 5, 6.7, 9]
print("Correct result:\t" + str([1, 6, 4, 6]))
print("Your result:\t" + str(histogram(data, num_bins=4)))

Python-compute the histogram of a set of data

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