dataframe - R data.table: How to sum variables by group based on a condition? -


let's have following r data.table (though i'm happy work base r, data.frame well)

library(data.table)  dt = data.table(category=c("first","first","first","second","third", "third", "second"), frequency=c(10,15,5,2,14,20,3), times = c(0, 0, 0, 3, 3, 1))  > dt    category frequency times 1:    first        10     0 2:    first        15     0 3:    first         5     0 4:   second         2     3 5:    third        14     3 6:    third        20     1 7:   second         3     0

if wished sum frequencies category, use following:

data[, sum(frequency), = category]

however, let's wanted sum frequency category if , if times non-zero , not equal na?

how 1 make sum conditional based on values of separate column?

edit: apologies obvious question. quick addition: if elements of column strings?

e.g. 

> dt    category frequency times 1:    first        ten    0 2:    first        ten    0 3:    first        5   0 4:   second        5   3 5:    third        5   3 6:    third        5   1 7:   second        ten    0

sum() not calculate frequencies of ten versus five

remember logic of data.table: dt[i, j, by], take dt, subset rows using i, calculate j grouped by.

dt[times != 0 & !is.na(times), sum(frequency), = category]    category v1 1:   second  2 2:    third 34

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