user21 - 10 months ago 35

Python 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

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)))
```