res = pd.to_numeric(df[0], errors="coerce") # float

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
plt.rcParams["font.sans-serif"] = ["SimHei"]
plt.rcParams["axes.unicode_minus"] = False

data = [[1,"2", "3"],[2, "a"]]
df = pd.DataFrame(data).T
# res = pd.to_numeric(df[0], errors="ignore")  # 已弃用ignore 不改变该值 其他值改为num 整体是混合类型object
res = pd.to_numeric(df[0], errors="coerce")  # float
print(res, type(res))