rdrecord: correctly infer length for multi-frequency records.

If the header file does not specify the record length, it must be
inferred from the size of the signal file (dividing the data length by
the number of samples per frame.)

Previously, this calculation assumed that tsamps_per_frame == n_sig,
which is not necessarily the case.  Correctly calculate the total spf
for the first signal file and use that as the divisor, rather than the
number of signals.  Rename the "n_sig" parameter of _infer_sig_len to
tsamps_per_frame accordingly.

Author: Benjamin Moody

wfdb/io/_signal.py

@@ -2059,7 +2059,7 @@ def describe_list_indices(full_list):
     return unique_elements, element_indices
 
 
-def _infer_sig_len(file_name, fmt, n_sig, dir_name, pn_dir=None):
+def _infer_sig_len(file_name, fmt, tsamps_per_frame, dir_name, pn_dir=None):
     """
     Infer the length of a signal from a dat file.
 
@@ -2069,8 +2069,8 @@ def _infer_sig_len(file_name, fmt, n_sig, dir_name, pn_dir=None):
         Name of the dat file.
     fmt : str
         WFDB fmt of the dat file.
-    n_sig : int
-        Number of signals contained in the dat file.
+    tsamps_per_frame : int
+        Total number of samples per frame contained in the dat file.
     dir_name : str
         The full directory where the dat file(s) are located, if the dat
         file(s) are local.
@@ -2081,11 +2081,11 @@ def _infer_sig_len(file_name, fmt, n_sig, dir_name, pn_dir=None):
     Returns
     -------
     sig_len : int
-        The length of the signal.
+        The length of the signal file in frames.
 
     Notes
     -----
-    sig_len * n_sig * bytes_per_sample == file_size
+    sig_len * tsamps_per_frame * bytes_per_sample == file_size
 
     """
     if pn_dir is None:
@@ -2094,7 +2094,7 @@ def _infer_sig_len(file_name, fmt, n_sig, dir_name, pn_dir=None):
         file_size = download._remote_file_size(file_name=file_name,
                                                pn_dir=pn_dir)
 
-    sig_len = int(file_size / (BYTES_PER_SAMPLE[fmt] * n_sig))
+    sig_len = int(file_size / (BYTES_PER_SAMPLE[fmt] * tsamps_per_frame))
 
     return sig_len
 

wfdb/io/record.py

@@ -3441,9 +3441,18 @@ def rdrecord(record_name, sampfrom=0, sampto=None, channels=None,
             if record.n_sig == 0:
                 record.sig_len = 0
             else:
+                # Calculate total number of samples per frame in the
+                # first dat file.
+                tsamps_per_frame = 0
+                for fname, spf in zip(record.file_name,
+                                      record.samps_per_frame):
+                    if fname == record.file_name[0]:
+                        tsamps_per_frame += spf
+
+                # Calculate length from size of the dat file.
                 record.sig_len = _signal._infer_sig_len(
                     file_name=record.file_name[0], fmt=record.fmt[0],
-                    n_sig=record.file_name.count(record.file_name[0]),
+                    tsamps_per_frame=tsamps_per_frame,
                     dir_name=dir_name, pn_dir=pn_dir)
         sampto = record.sig_len