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How to fix "X must have 2 or fewer dimensions" error in pyplot from matplotlib using the .boxplot function?

I want to create one figure with 2 boxplots using pyplot from matplotlib in python.

I am working with the iris dataset which provides petal length for 150 flowers from three types: Setosa, Versicolor, Virginica. I want to create one boxplot for the petal length of Setosa and one boxplot for the petal length of Versicolor, all on the same figure.

I based my code on this tutorial: https://matplotlib.org/gallery/pyplots/boxplot_demo_pyplot.html#sphx-glr-gallery-pyplots-boxplot-demo-pyplot-py

import numpy as np
import pandas as pd
from sklearn.datasets import load_iris
from matplotlib import pyplot as plt
# From the iris dataset I create a dataframe which contains only the features 
# of the flowers (sepal length, sepal width, petal length, petal width and the 
# flower type. 
data = load_iris()
X= data["data"]
y = data ["target"]
iris=pd.DataFrame(X)
iris["target"]=y
iris.columns=data['feature_names']+["target"]
iris["target"]=iris["target"].apply(lambda x:'Setosa' if x == 0 else 'Versicolor' if x == 1 else 'Virginica')
# I create my sub-dataframes which each contain the petal length of one type of flower 
ar1 = np.array(iris.loc[lambda iris: iris["target"] == "Setosa", ["petal width (cm)"]])
ar2 = np.array(iris.loc[lambda iris: iris["target"] == "Versicolor", ["petal width (cm)"]])
# This works: 
fig, ax = plt.subplots()
ax.boxplot(ar1)
plt.show()
# But this doesn't work:
data1 = [ar1, ar2] 
fig, ax = plt.subplots()
ax.boxplot(data1)
plt.show()
I expect a figure with 2 boxplots. Instead I get the error: "ValueError: X must have 2 or fewer dimensions". However ar1 and ar2 have 2 dimensions exactly like shown in the matplotlib exemple mentioned above. 
Thank you very much for your help,
The problem is that 
ar1 = np.array(iris.loc[lambda iris: iris["target"] == "Setosa", ["petal width (cm)"]])
creates a 2D array of shape (50,1). So what you can do is flatten the array first, 
data1 = [ar1.flatten(), ar2.flatten()] 
fig, ax = plt.subplots()
ax.boxplot(data1)
        
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