diff --git a/_episodes/04-modelling.md b/_episodes/04-modelling.md
index 5afc09c..2720304 100644
--- a/_episodes/04-modelling.md
+++ b/_episodes/04-modelling.md
@@ -39,7 +39,7 @@ from sklearn.linear_model import LinearRegression
 reg = LinearRegression()
 
 # use a single feature (apache score)
-X = cohort.apachescore.values.reshape((len(cohort.apachescore.values), 1))
+X = cohort.apachescore.values.reshape(-1, 1)
 y = cohort.actualhospitalmortality_enc.values
 
 # fit the model to our data
diff --git a/_episodes/05-validation.md b/_episodes/05-validation.md
index 39927ee..2f40b1f 100644
--- a/_episodes/05-validation.md
+++ b/_episodes/05-validation.md
@@ -50,9 +50,9 @@ y = cohort[outcome]
 x_train, x_test, y_train, y_test = train_test_split(X, y, train_size = 0.7, random_state = 42)
 
 # restructure data for input into model
-x_train = x_train.values.reshape((len(x_train.values), 1))
+x_train = x_train.values.reshape(-1, 1)
 y_train = y_train.values.ravel()
-x_test = x_test.values.reshape((len(x_test.values), 1))
+x_test = x_test.values.reshape(-1, 1)
 y_test = y_test.values.ravel()
 
 # train model
diff --git a/_episodes/06-evaluation.md b/_episodes/06-evaluation.md
index 4356599..cb5d5aa 100644
--- a/_episodes/06-evaluation.md
+++ b/_episodes/06-evaluation.md
@@ -44,9 +44,9 @@ y = cohort[outcome]
 x_train, x_test, y_train, y_test = train_test_split(X, y, train_size = 0.7, random_state =  42)
 
 # restructure data for input into model
-x_train = x_train.values.reshape((len(x_train.values), 1))
+x_train = x_train.values.reshape(-1, 1)
 y_train = y_train.values.ravel()
-x_test = x_test.values.reshape((len(x_test.values), 1))
+x_test = x_test.values.reshape(-1, 1)
 y_test = y_test.values.ravel()
 
 # train model
diff --git a/_episodes/07-bootstrapping.md b/_episodes/07-bootstrapping.md
index 63730aa..33f3896 100644
--- a/_episodes/07-bootstrapping.md
+++ b/_episodes/07-bootstrapping.md
@@ -55,9 +55,9 @@ y = cohort[outcome]
 x_train, x_test, y_train, y_test = train_test_split(X, y, train_size = 0.7, random_state = 42)
 
 # restructure data for input into model
-x_train = x_train.values.reshape((len(x_train.values), 1))
+x_train = x_train.values.reshape(-1, 1)
 y_train = y_train.values.ravel()
-x_test = x_test.values.reshape((len(x_test.values), 1))
+x_test = x_test.values.reshape(-1, 1)
 y_test = y_test.values.ravel()
 
 # train model