如何在字典中的数据帧上迭代期间创建和填充列

Question

我在字典里有一个.csv文件，里面有一些数据。我想做的是迭代dataframe（它本身在dictionary中）中的特定列（使用字符串），并根据条件在该行（但在新列）中指定特定的数字

import os
from os import listdir
from os.path import isfile, join
import pandas as pd

### INPUT DIRECTORY
path="folder"


### READING .csv FILES TO THE "dictionary"
files=[f.split('.')[0] for f in listdir(path) if isfile(join(path, f))]
dictionary={}
for file in files:
    dictionary[file]=pd.read_csv(path+'/'+file+'.csv')

### DROPPING 2ND ROW
results={}
for df in dictionary:
    results[str(df)+'_CONSTANT_VAR'] = dictionary[df]
    results[str(df)+'_CONSTANT_VAR'] = results[str(df)+'_CONSTANT_D_SHALE_VAR'].iloc[1:]



for df in results:
    for i in results[str(df)]['FORMATION']:
        if i=='BAL6':
            results[str(df)]['VAR'][i]=10  ### HERE I WANT TO ADD VALUE TO THE NEW COLUMN

不幸的是，代码只是将“10”放在所有地方，而不仅仅放在满足条件的行上。 知道为什么会这样吗？如何按照我想要的方式去做

---

此外，还会弹出一个错误：

<input>:27: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

---

输入数据：

wellName    DEPTH   FORMATION   depth2
well name   1000    bal0.5     123
well name   2000    bal1       124
well name   3000    bal0.6     125
well name   4000    bal2       126
well name   5000    bal0.7     127
well name   6000    bal3       128
well name   7000    bal0.8     129
well name   8000    bal4       130
well name   9000    bal0.9     131
well name   10000   bal5       132
well name   11000   bal0.10    133
well name   12000   bal6       134
well name   13000   bal0.11    135

输出IAM获取：

wellName    DEPTH   FORMATION   depth2 VAR
well name   1000    bal0.5     123     10
well name   2000    bal1       124     10
well name   3000    bal0.6     125     10
well name   4000    bal2       126     10
well name   5000    bal0.7     127     10
well name   6000    bal3       128     10
well name   7000    bal0.8     129     10
well name   8000    bal4       130     10
well name   9000    bal0.9     131     10
well name   10000   bal5       132     10
well name   11000   bal0.10    133     10
well name   12000   bal6       134     10
well name   13000   bal0.11    135     10

我想要的输出：

wellName    DEPTH   FORMATION   depth2 VAR
well name   1000    bal0.5     123     
well name   2000    bal1       124     
well name   3000    bal0.6     125     
well name   4000    bal2       126     
well name   5000    bal0.7     127     
well name   6000    bal3       128     
well name   7000    bal0.8     129     
well name   8000    bal4       130     
well name   9000    bal0.9     131     
well name   10000   bal5       132     
well name   11000   bal0.10    133     
well name   12000   bal6       134     10   ### VALUE ADDED ONLY HERE
well name   13000   bal0.11    135     

Answer 1

给定数据帧df（如输入数据中所示），您可以使用以下命令有条件地指定一个新列VAR或在列VAR中指定一个值

df.loc[(df.FORMATION == 'bal6'), 'VAR'] = 10

您得到的“error”消息实际上是一个警告，您为数据帧的副本指定了一个新值，并且数据帧本身不会被更改。这称为链式索引并解释为here