MIT-LCP / MIT-LCP/wfdb-python

Correct sampto behaviour using rdsamp and rdann?

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Description

When reading the signal with rdsamp and the corresponding annotations with rdann using the same sampto value results in an IndexError when accessing the signal array it includes an annotation outside the array.

In the example below, to read the first 100 entries, sampto must be 100. If using the same value for the annotations up to and including 100 are read, rather than stopping at 99 (i.e., the 100th entry in a 0-indexed array).

Is this the expected behaviour?

Using: python 3.9.18 with wfdb 4.1.2

import numpy as np
import wfdb

# create test data
n = 250
test_sig = np.zeros((n, 1))
test_sig[:, 0] = np.linspace(0, 1, n)
print(f'original shape: {test_sig.shape}')

# write to file
wfdb.wrsamp('test', fs = 250, units=['mV'], sig_name=['test'], p_signal=test_sig, fmt=['16'])

# create annotation and write
wfdb.Annotation(
    record_name='test', 
    extension='atr',
    sample=np.array([0, 99, 100, 249]), 
    symbol=['N', 'N', 'N', 'N']
).wrann()

samp_from = 0
samp_to = 100

# read values
values, _ = wfdb.rdsamp('test', sampfrom=samp_from, sampto=samp_to)
print(f'sampto shape: {values.shape}')


atr_1 = wfdb.rdann('test', extension='atr', sampfrom=samp_from, sampto=samp_to, shift_samps=True)
print(f'samples: {atr_1.sample}')
# IndexError
# print(f'values at samples: {values[atr_1.sample, :]}')

samp_to_minus_1 = samp_to - 1
atr_2 = wfdb.rdann('test', extension='atr', sampfrom=samp_from, sampto=samp_to_minus_1, shift_samps=True)
print(f'samples: {atr_2.sample}')
# No IndexError
# print(f'values at samples: {values[atr_2.sample, :]}')

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Research direction

Start by running the supplied Python reproduction with wfdb.rdsamp and wfdb.rdann, using the same sampto value and the sample at index 100. Trace how each entry point handles the upper boundary; done means their range semantics are consistent and indexing returned annotations does not raise IndexError.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
backend-api-design
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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