我的目标是创建一个i，其中包含ColumnName_1个名为ColumnName_i的列i = 3 - ＆gt; structure(list(ColumnName_1 = c(0, 0, 0), ColumnName_2 = c(0,
0, 0), ColumnName_3 = c(0, 0, 0)), .Names = c("ColumnName_1",
"ColumnName_2", "ColumnName_3"), row.names = c(NA, -3L), class = "data.frame")
结果将是assign：
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.content.ContextCompat;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.Window;
import android.view.WindowManager;
import android.widget.ArrayAdapter;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class Manager extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener,View.OnClickListener {
Data dat=new Data();
private ImageView imageView;
private ImageButton logout,viewlibrary;
TextView headerTitle;
FragmentManager fragmentManager;
String manager="";
@Override
protected void onCreate(Bundle savedInstanceState) {
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_manager);
headerTitle=(TextView)findViewById(R.id.headertitle);
headerTitle.setText("Manager's Panel");
TextView tv=(TextView)findViewById(R.id.usrmsgman);
tv.setText("USER : "+dat.getUser());
logout=(ImageButton)findViewById(R.id.logoutbut);
viewlibrary=(ImageButton)findViewById(R.id.libview);
/*
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
*/
ListView lv=(ListView)findViewById(R.id.listView);
Downloader d=new Downloader(this,dat.getHost()+"managerhome.php",lv);
d.execute();
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
/*
---------------------------------------------------------------------------
---------------------------------------------------------------------------
---------------------------------------------------------------------------
What to do here?
---------------------------------------------------------------------------
---------------------------------------------------------------------------
---------------------------------------------------------------------------
*/
});
logout.setOnClickListener(this);
viewlibrary.setOnClickListener(this);
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId())
{
case R.id.logoutbut :
SharedPreferences sp=getSharedPreferences("Login", 0);
SharedPreferences.Editor Ed=sp.edit();
Ed.putString("Unm",null );
Ed.putString("Psw",null);
Ed.putString("app",null);
Ed.commit();
this.finish();
startActivity(new Intent(Manager.this,Login.class));
break;
case R.id.libview :
startActivity(new Intent(this,ViewLibrary.class));
break;
}
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
public void removeFragment(Fragment fragment){
android.support.v4.app.FragmentManager fragmentManager = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.remove(fragment);
fragmentTransaction.commit();
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_issue) {
IssueFragment issueFragment=new IssueFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,issueFragment).commit();
} else if (id == R.id.nav_reissue) {
RIssueFragment rissueFragment = new RIssueFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment, rissueFragment).commit();
} else if (id == R.id.nav_retbook) {
ReturnFragment returnFragment= new ReturnFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,returnFragment).commit();
} else if (id == R.id.nav_search) {
SearchFragment searchFragment= new SearchFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,searchFragment).commit();
} else if (id == R.id.nav_abtApp) {
AbtAppFragment abtAppFragment=new AbtAppFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,abtAppFragment).commit();
} else if (id == R.id.nav_abtDev) {
AbtDevFragment abtDevFragment= new AbtDevFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,abtDevFragment).commit();
} else if (id == R.id.nav_view_mem) {
ViewMemberFragment viewMemberFragment= new ViewMemberFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,viewMemberFragment).commit();
} else if (id == R.id.nav_log) {
LogFragment logFragment= new LogFragment();
FragmentManager manager=getSupportFragmentManager();
fragmentManager=manager;
manager.beginTransaction().replace(R.id.reloutForFragment,logFragment).commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
我从其他问题中了解到其他主题不建议使用Intent intent = getIntent();
finish();
startActivity(intent);
，但这是我目前看到的唯一解决方案。
答案 0 :(得分：1)
这是一种方法，它使用replicate和data.frame构建一个空数据框。无论你想要什么尺寸（使用数字变量），然后使用setNames来提供变量名。
setNames(data.frame(replicate(3, numeric(3), simplify=FALSE)),
paste0("colName", seq_len(3)))
colName1 colName2 colName3
1 0 0 0
2 0 0 0
3 0 0 0
复制的第一个参数提供列数，第二个参数numeric(3)提供行数。
答案 1 :(得分：1)
我们可以使用以下内容，假设您需要m行和n列：
data.frame(matrix(0, nrow = m, ncol = n,
dimnames = list(NULL, paste0("ColumnName_", 1:n))) )
所有其他答案都使用循环来创建列，而此解决方案是完全矢量化的。
答案 2 :(得分：1)
lapply的版本。
i <- 3
setNames(as.data.frame(lapply(1:i, function(k) c(0, 0, 0))),
paste("ColumnName_", 1:i, sep = ""))