我有两个数据框：
Dataframe A:
Col1 Col2 Value
A X 1
A Y 2
B X 3
B Y 2
C X 5
C Y 4
Dataframe B:
Col1
A
B
C
我需要为数据帧A的Col2中的每个值（在本例中为X和Y）的每个值添加到数据帧B中，并在合并两个数据帧后在“值”列中填充值Col1。就是这样：
Col1 X Y
A 1 2
B 3 2
C 5 4
非常感谢您的帮助！
答案 0 :(得分：0)
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import '../models/http_exception.dart';
class Auth with ChangeNotifier {
String _token;
//tokens only last about an hour
DateTime _expiryDate;
String _userId;
Future<void> _authenticate(
String email, String password, String urlSegment) async {
final url = 'UrlIsCorrectInMyCode'; //changed on purpose
try {
final response = await http.post(
url,
body: json.encode(
{
'email': email,
'password': password,
'returnSecureToken': true,
},
),
);
final responseData = json.decode(response.body);
if(responseData['error'] != null){
throw HttpException(responseData['error']['message']);
}
} catch (error) {
throw error;
}
}
Future<void> signUp(String email, String password) async {
return _authenticate(email, password, 'signUp');
//in order for the progress indicator to be shown
//it must be returned so that it takes the future of
//_authenticate and not just any future
}
Future<void> login(String email, String password) async {
return _authenticate(email, password, 'signInWithPassword');
}
}
如果在Col2中要有100个不同的值，则可以循环调用上述两行，如下所示：
import 'dart:math';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../providers/auth.dart';
import '../models/http_exception.dart';
enum AuthMode { Signup, Login }
class AuthScreen extends StatelessWidget {
static const routeName = '/auth';
@override
Widget build(BuildContext context) {
final deviceSize = MediaQuery.of(context).size;
// final transformConfig = Matrix4.rotationZ(-8 * pi / 180);
// transformConfig.translate(-10.0);
return Scaffold(
// resizeToAvoidBottomInset: false,
body: Stack(
children: <Widget>[
Container(
decoration: BoxDecoration(
gradient: LinearGradient(
colors: [
Color.fromRGBO(215, 117, 255, 1).withOpacity(0.5),
Color.fromRGBO(255, 188, 117, 1).withOpacity(0.9),
],
begin: Alignment.topLeft,
end: Alignment.bottomRight,
stops: [0, 1],
),
),
),
SingleChildScrollView(
child: Container(
height: deviceSize.height,
width: deviceSize.width,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Flexible(
child: Container(
margin: EdgeInsets.only(bottom: 20.0),
padding:
EdgeInsets.symmetric(vertical: 8.0, horizontal: 94.0),
transform: Matrix4.rotationZ(-8 * pi / 180)
..translate(-10.0),
//transform allows to rotate or scale a box
//the '..' operator allows you to return the matrix4
//object that rotationZ provides instead of the void
//response that .translate provides
// ..translate(-10.0),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(20),
color: Colors.deepOrange.shade900,
boxShadow: [
BoxShadow(
blurRadius: 8,
color: Colors.black26,
offset: Offset(0, 2),
)
],
),
child: Text(
'MyShop',
style: TextStyle(
color:
Theme.of(context).accentTextTheme.headline6.color,
fontSize: 50,
fontFamily: 'Anton',
fontWeight: FontWeight.normal,
),
),
),
),
Flexible(
flex: deviceSize.width > 600 ? 2 : 1,
child: AuthCard(),
),
],
),
),
),
],
),
);
}
}
class AuthCard extends StatefulWidget {
const AuthCard({
Key key,
}) : super(key: key);
@override
_AuthCardState createState() => _AuthCardState();
}
class _AuthCardState extends State<AuthCard> {
final GlobalKey<FormState> _formKey = GlobalKey();
AuthMode _authMode = AuthMode.Login;
Map<String, String> _authData = {
'email': '',
'password': '',
};
var _isLoading = false;
final _passwordController = TextEditingController();
void _showErrorDialog(String message) {
showDialog(
context: context,
builder: (ctx) => AlertDialog(
title: Text("An error occured"),
content: Text(message),
actions: [
FlatButton(
child: Text("Okay"),
onPressed: () {
Navigator.of(ctx).pop();
},
),
],
),
);
}
Future<void> _submit() async {
if (!_formKey.currentState.validate()) {
// Invalid!
return;
}
_formKey.currentState.save();
setState(() {
_isLoading = true;
});
try {
if (_authMode == AuthMode.Login) {
await Provider.of<Auth>(context, listen: false).login(
_authData['email'],
_authData['password'],
);
} else {
await Provider.of<Auth>(context, listen: false).signUp(
_authData['email'],
_authData['password'],
);
}
} on HttpException catch (error) {
//this means a special type of error is thrown
//this acts as a filter for the type of error
var errorMessage = 'Authentication failed.';
if (error.toString().contains("EMAIL_EXISTS")) {
errorMessage = 'This email address is already in use';
} else if (error.toString().contains('INVALID_EMAIL')) {
errorMessage = 'This is not a valid email address.';
} else if (error.toString().contains('WEAK_PASSWORD')) {
errorMessage = 'This password is too weak.';
} else if (error.toString().contains('EMAIL_NOT_FOUND')) {
errorMessage = 'Could not find a user with that email.';
} else if (error.toString().contains('INVALID_PASSWORD')) {
errorMessage = 'Invalid password.';
}
_showErrorDialog(errorMessage);
} catch (error) {
const errorMessage = 'Could not authenticate. Please try again.';
_showErrorDialog(errorMessage);
}
setState(() {
_isLoading = false;
});
}
void _switchAuthMode() {
if (_authMode == AuthMode.Login) {
setState(() {
_authMode = AuthMode.Signup;
});
} else {
setState(() {
_authMode = AuthMode.Login;
});
}
}
@override
Widget build(BuildContext context) {
final deviceSize = MediaQuery.of(context).size;
return Card(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10.0),
),
elevation: 8.0,
child: Container(
height: _authMode == AuthMode.Signup ? 320 : 260,
constraints:
BoxConstraints(minHeight: _authMode == AuthMode.Signup ? 320 : 260),
width: deviceSize.width * 0.75,
padding: EdgeInsets.all(16.0),
child: Form(
key: _formKey,
child: SingleChildScrollView(
child: Column(
children: <Widget>[
TextFormField(
decoration: InputDecoration(labelText: 'E-Mail'),
keyboardType: TextInputType.emailAddress,
validator: (value) {
if (value.isEmpty || !value.contains('@')) {
return 'Invalid email!';
} else {
return null;
}
},
onSaved: (value) {
_authData['email'] = value;
},
),
TextFormField(
decoration: InputDecoration(labelText: 'Password'),
obscureText: true,
controller: _passwordController,
validator: (value) {
if (value.isEmpty || value.length < 5) {
return 'Password is too short!';
} else {
return null;
}
},
onSaved: (value) {
_authData['password'] = value;
},
),
if (_authMode == AuthMode.Signup)
TextFormField(
enabled: _authMode == AuthMode.Signup,
decoration: InputDecoration(labelText: 'Confirm Password'),
obscureText: true,
//this allows stars to mask the input
validator: _authMode == AuthMode.Signup
? (value) {
if (value != _passwordController.text) {
return 'Passwords do not match!';
} else {
return null;
}
}
: null,
),
SizedBox(
height: 20,
),
if (_isLoading)
CircularProgressIndicator()
else
RaisedButton(
child:
Text(_authMode == AuthMode.Login ? 'LOGIN' : 'SIGN UP'),
onPressed: _submit,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(30),
),
padding:
EdgeInsets.symmetric(horizontal: 30.0, vertical: 8.0),
color: Theme.of(context).primaryColor,
textColor: Theme.of(context).primaryTextTheme.button.color,
),
FlatButton(
child: Text(
'${_authMode == AuthMode.Login ? 'SIGNUP' : 'LOGIN'} INSTEAD'),
onPressed: _switchAuthMode,
padding: EdgeInsets.symmetric(horizontal: 30.0, vertical: 4),
materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
//reduces the amount of surface area that is tappable
textColor: Theme.of(context).primaryColor,
),
],
),
),
),
),
);
}
}
您将获得相同的输出：
B['X'] = A.loc[A['Col2'] == 'X', 'Value'].reset_index(drop = True)
B['Y'] = A.loc[A['Col2'] == 'Y', 'Value'].reset_index(drop = True)
Col1 X Y
0 A 1 2
1 B 3 2
2 C 5 4