diff --git a/extraction/extract_item_into_dict.py b/extraction/extract_item_into_dict.py
index 5d70a50edfb9e786afd922a89d5675b32318c331..d3baf6f37eda324ff29e0bbbd0a8927211128a33 100644
--- a/extraction/extract_item_into_dict.py
+++ b/extraction/extract_item_into_dict.py
@@ -1,4 +1,5 @@
 """This file tries to split one matlab item into a dictionnary"""
+import numpy as np
 
 
 def _convert_matlab_datetime_vector_to_utc(date_vector):
@@ -70,26 +71,26 @@ def extract_impedance_from_item(item):
     dict_item["datetime"] = _convert_matlab_datetime_vector_to_utc(item[2][0])
 
     dict_item["sense_current"] = item[3][0][0][0][0]  # Current in sense branch (Amps)| Complexes
-    dict_item["sense_current_real"] = [complx.real for complx in dict_item["sense_current"]]
-    dict_item["sense_current_imag"] = [complx.imag for complx in dict_item["sense_current"]]
+    dict_item["sense_current_real"] = np.array([complx.real for complx in dict_item["sense_current"]])
+    dict_item["sense_current_imag"] = np.array([complx.imag for complx in dict_item["sense_current"]])
 
     dict_item["battery_current"] = item[3][0][0][1][0]  # Current in battery branch (Amps)| Complexes
-    dict_item["battery_current_real"] = [complx.real for complx in dict_item["battery_current"]]
-    dict_item["battery_current_imag"] = [complx.imag for complx in dict_item["battery_current"]]
+    dict_item["battery_current_real"] = np.array([complx.real for complx in dict_item["battery_current"]])
+    dict_item["battery_current_imag"] = np.array([complx.imag for complx in dict_item["battery_current"]])
 
     dict_item["current_ratio"] = item[3][0][0][2][0]  # Ratio of the above currents| Complexes
-    dict_item["current_ratio_real"] = [complx.real for complx in dict_item["current_ratio"]]
-    dict_item["current_ratio_imag"] = [complx.imag for complx in dict_item["current_ratio"]]
+    dict_item["current_ratio_real"] = np.array([complx.real for complx in dict_item["current_ratio"]])
+    dict_item["current_ratio_imag"] = np.array([complx.imag for complx in dict_item["current_ratio"]])
 
     # Battery impedance (Ohms) computed from raw data| Complexes
-    dict_item["battery_impedance"] = [val[0] for val in item[3][0][0][3]]
-    dict_item["battery_impedance_real"] = [complx.real for complx in dict_item["battery_impedance"]]
-    dict_item["battery_impedance_imag"] = [complx.imag for complx in dict_item["battery_impedance"]]
+    dict_item["battery_impedance"] = np.array([val[0] for val in item[3][0][0][3]])
+    dict_item["battery_impedance_real"] = np.array([complx.real for complx in dict_item["battery_impedance"]])
+    dict_item["battery_impedance_imag"] = np.array([complx.imag for complx in dict_item["battery_impedance"]])
 
     # Calibrated and smoothed battery impedance (Ohms)| Complexes
-    dict_item["rectified_impedance"] = [val[0] for val in item[3][0][0][4]]
-    dict_item["rectified_impedance_real"] = [complx.real for complx in dict_item["rectified_impedance"]]
-    dict_item["rectified_impedance_imag"] = [complx.imag for complx in dict_item["rectified_impedance"]]
+    dict_item["rectified_impedance"] = np.array([val[0] for val in item[3][0][0][4]])
+    dict_item["rectified_impedance_real"] = np.array([complx.real for complx in dict_item["rectified_impedance"]])
+    dict_item["rectified_impedance_imag"] = np.array([complx.imag for complx in dict_item["rectified_impedance"]])
 
     dict_item["re"] = item[3][0][0][5][0][0]  # Estimated electrolyte resistance (Ohms)| float_
     dict_item["rct"] = item[3][0][0][6][0][0]  # Estimated charge transfer resistance (Ohms)| float_