R Data.Table: In-memory left join multiple columns from left and right side -


i want merge 2 data tables on multiple columns using data table. 

## 2 tables <- data.table(a = 1:4, b = 12:15, c = 10:13)     b  c 1: 1 12 10 2: 2 13 11 3: 3 14 12 4: 4 15 13  b <- data.table(a = 1:3, b = 12:14, d = 10:12, e = 10:12)     b  d  e 1: 1 12 10 10 2: 2 13 11 11 3: 3 14 12 12

i result:

a <- merge(a, b, = c('a', 'b'), all.x = t)     b  c  d  e 1: 1 12 10 10 10 2: 2 13 11 11 11 3: 3 14 12 12 12 4: 4 15 13 na na

this answer showed data table can edit data frame in-memory, it's more efficient when using large data sets. code suggested is

a[b, bb:=i.b, on='a']

how can alter code data frame merged in-memory, , result same above?

if meant join. here i.d or i.e not needed columns unique in 'b'

nm1 <- setdiff(names(b), names(a))  a[b, (nm1) :=  mget(nm1), on = .(a, b)] #    b  c  d  e #1: 1 12 10 10 10 #2: 2 13 11 11 11 #3: 3 14 12 12 12 #4: 4 15 13 na na

Comments

Post a Comment

Popular posts from this blog

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

sql server - Why does Linq-to-SQL add unnecessary COUNT()? -

here tables: create table customer ( cid int primary key, name varchar(32) ) create table ord ( oid int primary key, cid int foreign key references customer, address varchar(20) ) here's linq-to-sql statement: var aaa = c in db.customer select new { c, o = c.ord.tolist() }; and here's inexplicable query generated linq-to-sql: select [t0].[cid] [cid], [t0].[name] [name], [t1].[oid] [oid], [t1].[cid] [cid2], [t1].[address] [address], (select count(*) [dbo].[ord] [t2] [t2].[cid] = [t0].[cid]) [value] [dbo].[customer] [t0] left outer join [dbo].[ord] [t1] on [t1].[cid] = [t0].[cid] order [t0].[cid], [t1].[oid] i want understand how rid of count(*) part. it's entirely uncalled for! linq needs count(*) in order determine number of entries returned o = c.ord.tolist() .
Read more