diff --git a/volia/core/data.py b/volia/core/data.py
index 4c1bdae..300b266 100644
--- a/volia/core/data.py
+++ b/volia/core/data.py
@@ -4,41 +4,104 @@ Data management input/output
 
 # Import packages and modules
 import numpy as np
+import sys
 
 # Defining some types
 from typing import List, Dict
 KeyToList = Dict[str, List[str]]
+KeyToLabels = Dict[str, List[str]]
+KeyToIntLabels = Dict[str, List[int]]
 KeyToFeatures = Dict[str, List[float]]
 
 
 def read_lst(file_path: str) -> KeyToList:
     '''
     Read lst file with this structure:
-    [id] [value1] [value2] ... [value n]
+    [id_1]
+    [id_2]
+    ...
+    [id_n]
+    
+    Return a list of ids.
+    '''
+    lst = []
+    with open(file_path, "r") as f:
+        for line in f:
+            lst.append(line.replace("\n", ""))
+    return lst
+
+
+def read_id_values(file_path: str, value_type=str):
+    '''
+    Read file where each line is an id with its corresponding values:
+    [id_1] [value_1_1] [value_1_2] ... [value_1_k]
+    [id_2] [value_2_1] [value_2_2] ... [value_2_k]
+    ...
+    [id_n] [value_n_1] [value_n_2] ... [value_n_k]
+
+    where values are value_type type.
 
-    This is a basic function reused by others like read_features.
-    returns a dictionary with id as key and a list of value as corresponding values
+    Used in many reader functions with specific value_type.
+    Return a dictionary with id as key and values as associated values.
     '''
-    # KeyToList type variable
-    key_to_list = dict() 
+    id_values = {}
     with open(file_path, "r") as f:
         for line in f:
             splited = line.replace("\n", "").split(" ")
-            id = splited[0]
-            values = splited[1:]
-            key_to_list[id] = values
-    return key_to_list
+            id_values[splited[0]] = np.asarray(splited[1:], dtype=value_type)
+    return id_values
 
 
 def read_features(file_path: str) -> KeyToFeatures:
     '''
+    Read features files with the following structure:
+    [id_1] [value_1_1] [value_1_2] ... [value_1_k]
+    [id_2] [value_2_1] [value_2_2] ... [value_2_k]
+    ...
+    [id_n] [value_n_1] [value_n_2] ... [value_n_k]
+
+    where values are float
+
+    Returns a dictionary with id as key and a list of values as associated values
     '''
-    # KeyToFeatures type variable
-    key_to_features = dict()
-    # and the KeyToList
-    key_to_list = read_lst(file_path)
-    
-    for key_, list_ in key_to_list.items():
-        key_to_features[key_] = np.asarray(list_, dtype=float)
+    return read_id_values(file_path, float)
+
+
+def read_labels(file_path: str) -> KeyToLabels:
+    '''
+    Read features files with the following structure :
+    [id_1] [value_1_1] [value_1_2] ... [value_1_k]
+    [id_2] [value_2_1] [value_2_2] ... [value_2_k]
+    ...
+    [id_n] [value_n_1] [value_n_2] ... [value_n_k]
+
+    where values are int
+    '''
+    return read_id_values(file_path, str)
+
+
+def read_labels_integer(file_path: str) -> KeyToIntLabels:
+    '''
+    Read features files with the following structure :
+    [id_1] [value_1_1] [value_1_2] ... [value_1_k]
+    [id_2] [value_2_1] [value_2_2] ... [value_2_k]
+    ...
+    [id_n] [value_n_1] [value_n_2] ... [value_n_k]
+
+    where values are int
+    '''
+    return read_id_values(file_path, int)
+
+
+def write_line(id_, values=[], out=sys.stdout):
+    """
+    Write a line in list, labels or features files.
+    If you want to write a list, specify an empty
+    array for *values*. 
 
-    return key_to_features
\ No newline at end of file
+    Args:
+        id_ (str): id in string.
+        values (list, optional): list of values to write, features or labels. Defaults to [].
+        out (_io.TextIOWrapper, optional): . Defaults to sys.stdout.
+    """
+    out.write(str(id_) + " ".join(values) + "\n")
\ No newline at end of file