_reorder_bits method in ibmqbackend for real backends

qiskit/backends/ibmq/ibmqbackend.py

@@ -121,6 +121,8 @@ def run(self, q_job):
         job_result['name'] = qobj['id']
         job_result['backend'] = qobj['config']['backend_name']
         this_result = Result(job_result, qobj)
+        if not self.configuration['simulator']:
+            _reorder_bits(this_result)  # FIXME: remove this after Qobj
         return this_result
 
     @property
@@ -265,3 +267,58 @@ def _wait_for_job(job_id, api, wait=5, timeout=60):
                                   'status': job_result['qasms'][index]['status']})
     return {'job_id': job_id, 'status': job_result['status'],
             'result': job_result_return}
+
+
+def _reorder_bits(result):
+    """temporary fix for ibmq backends.
+    for every ran circuit, get reordering information from qobj
+    and apply reordering on result"""
+    for idx, circ in enumerate(result._qobj['circuits']):
+
+        # device_qubit -> device_clbit (how it should have been)
+        measure_dict = {op['qubits'][0]: op['clbits'][0]
+                        for op in circ['compiled_circuit']['operations']
+                        if op['name'] == 'measure'}
+
+        res = result._result['result'][idx]
+        counts_dict_new = {}
+        for item in res['data']['counts'].items():
+            # fix clbit ordering to what it should have been
+            bits = list(item[0])
+            bits.reverse()  # lsb in 0th position
+            count = item[1]
+            reordered_bits = list('x' * len(bits))
+            for device_clbit, bit in enumerate(bits):
+                if device_clbit in measure_dict:
+                    correct_device_clbit = measure_dict[device_clbit]
+                    reordered_bits[correct_device_clbit] = bit
+            reordered_bits.reverse()
+
+            # only keep the clbits specified by circuit, not everything on device
+            num_clbits = circ['compiled_circuit']['header']['number_of_clbits']
+            compact_key = reordered_bits[-num_clbits:]
+            compact_key = "".join([b if b != 'x' else '0'
+                                   for b in compact_key])
+
+            # insert spaces to signify different classical registers
+            cregs = circ['compiled_circuit']['header']['clbit_labels']
+            if sum([creg[1] for creg in cregs]) != num_clbits:
+                raise ResultError("creg sizes don't add up in result header.")
+            creg_begin_pos = []
+            creg_end_pos = []
+            acc = 0
+            for creg in reversed(cregs):
+                creg_size = creg[1]
+                creg_begin_pos.append(acc)
+                creg_end_pos.append(acc + creg_size)
+                acc += creg_size
+            compact_key = " ".join([compact_key[creg_begin_pos[i]:creg_end_pos[i]]
+                                    for i in range(len(cregs))])
+
+            # marginalize over unwanted measured qubits
+            if compact_key not in counts_dict_new:
+                counts_dict_new[compact_key] = count
+            else:
+                counts_dict_new[compact_key] += count
+
+        res['data']['counts'] = counts_dict_new