df.append() 没有附加到 DataFrame [英] df.append() is not appending to the DataFrame

问题描述

我制定了这个问题关于添加带有索引的行，但我还不清楚在没有索引的情况下如何/为什么会发生这种情况:

columnsList=['A','B','C','D']df8=pd.DataFrame(columns=columnsList)L=['value aa','value bb','value cc','value dd']s = pd.Series(dict(zip(df8.columns, L)))df8.append(s,ignore_index=True)df8.append(s,ignore_index=True)

我希望这里有一个 2X4 的数据框.然而没有添加任何值，也没有发生错误.

print(df8.shape)#>>>(0,4)

为什么没有加入系列，为什么没有报错?

<小时>

如果我尝试使用 LOC 添加一行，则会添加一个索引，

df8.loc[df8.index.max() + 1, :] = [4, 5, 6,7]打印(df8)

结果:

 A B C D南 4 5 6 7

我猜LOC和iLOC都不能用来追加没有索引名的行(即Loc加了索引名NaN，索引号高于数据库行数时不能使用iLoc)

解决方案

DataFrame.append 不是就地操作.从文档中，

<块引用>

DataFrame.append(other, ignore_index=False, verify_integrity=False, sort=None)

将 other 的行附加到此帧的末尾，返回一个新对象.不在此框架中的列将作为新列添加.

您需要将结果分配回来.

df8 = df8.append([s] * 2, ignore_index=True)df8A B C D0 值 aa 值 bb 值 cc 值 dd1 值 aa 值 bb 值 cc 值 dd

I formulated this question about adding rows WITH index, but it is not yet clear to me how/why this happens when there are no indexes:

columnsList=['A','B','C','D']
df8=pd.DataFrame(columns=columnsList)
L=['value aa','value bb','value cc','value dd']
s = pd.Series(dict(zip(df8.columns, L)))
df8.append(s,ignore_index=True)
df8.append(s,ignore_index=True)

I EXPECT HERE A 2X4 DATAFRAME. nevertheless no values where added, nor an error occurred.

print(df8.shape)
#>>> (0,4)

Why is the series not being added, and why is not given any error?

---

If I try to add a row with LOC, an index is added,

df8.loc[df8.index.max() + 1, :] = [4, 5, 6,7]
print(df8)

result:

     A  B  C  D
NaN  4  5  6  7

I guess neither LOC, nor iLOC could be used to append rows without index name (i.e. Loc adds the index name NaN, and iLoc can not be used when the index number is higher than the rows of the database)

解决方案

DataFrame.append is not an in-place operation. From the docs,

DataFrame.append(other, ignore_index=False, verify_integrity=False, sort=None)

Append rows of other to the end of this frame, returning a new object. Columns not in this frame are added as new columns.

You need to assign the result back.

df8 = df8.append([s] * 2, ignore_index=True)
df8
          A         B         C         D
0  value aa  value bb  value cc  value dd
1  value aa  value bb  value cc  value dd

这篇关于df.append() 没有附加到 DataFrame的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！