如何向 DataFrame 添加字符串值? [英] How do I add a string value to DataFrame?
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问题描述
string = 'cool'
df = pd.DataFrame(columns=['string_values'])
附加
df.append(string)
当我尝试将其附加到 df 时出现此错误.(是不是只针对数值数据?)
I get this error when I try to append it into df. (Is it only for numerical data?)
cannot concatenate object of type "<class 'str'>"; only pd.Series, pd.DataFrame, and pd.Panel (deprecated) objs are valid
我只想在数据框中添加一个字符串值 string = 'cool'
,但我收到此错误.
I just want to add a string value string = 'cool'
into the dataframe, but I get this error.
推荐答案
我认为最好使用 DataFrame
构造函数并分配一个元素列表:
I think best is use DataFrame
contructor and assign one element list:
string = 'cool'
df = pd.DataFrame([string], columns=['string_values'])
print (df)
string_values
0 cool
如果字符串是在循环中生成的,最好将它们附加到一个列表中,然后只传递给构造函数一次:
If strings are generated in loop best is append them to one list and then pass to constructor only once:
L = []
for x in range(3):
L.append(string)
df = pd.DataFrame(L, columns=['string_values'])
print (df)
string_values
0 cool
1 cool
2 cool
性能:
In [43]: %%timeit
...: L = []
...: for x in range(1000):
...: value1 = "dog" + str(x)
...: L.append(value1)
...:
...: df = pd.DataFrame(L, columns=['string_values'])
...:
1.29 ms ± 56.6 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
In [44]: %%timeit
...: df = pd.DataFrame(columns=['string_values'])
...: for x in range(1000):
...: value1 = "dog" + str(x)
...: df = df.append({'string_values': value1}, ignore_index=True)
...:
1.19 s ± 34.3 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
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