通过检查之前的行用值填充空槽

Question

我有一个这样的 DataFrame：

day  value  
1 HSE  
2 HSE   
3  
4  
5  
6 LSE  
7 LSE  
8  
9  
10

现在，我想通过检查之前的值来用值填充空槽。所以，我想将 3、4、5 设置为 "fromHSE" 和 8、9、10 "fromLSE"。

我这样试过：

e = "HSE"

for line in df:
    if df['value'] == "":
        if e == "HSE":
            df['value'] = "fromHSE"
        elif e == "LSE":
            df['value'] = "fromLSE"
    elif df['value'] == "HSE":
        e = "HSE"
    elif df['value'] == "LSE":
        e = "LSE"

但是我得到了错误：

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

希望你能帮帮我。

Answer 1

你可以先replace empty string to NaN, create mask with isnull and create new Series with ffill. Last add string from with mask:

df.value.replace('',np.NaN, inplace=True)
mask = df.value.isnull()
new = df.value.ffill()
print (new.mask(mask, 'from' + new))
0        HSE
1        HSE
2    fromHSE
3    fromHSE
4    fromHSE
5        LSE
6        LSE
7    fromLSE
8    fromLSE
9    fromLSE
Name: value, dtype: object

通过检查之前的行用值填充空槽

Fill empty slot with value by checking the line before

string

dataframe

python-3.x

empty-list

pandas