r - using eval in data.table -



r - using eval in data.table -

i'm trying understand behaviour of eval in data.table "frame".

with next data.table:

set.seed(1) foo = data.table(var1=sample(1:3,1000,r=t), var2=rnorm(1000), var3=sample(letters[1:5],1000,replace = t))

i'm trying replicate instruction

foo[var1==1 , sum(var2) , by=var3]

using function of eval:

eval1 = function(s) eval( parse(text=s) ,envir=sys.parent() )

as can see, test 1 , 3 working, don't understand "correct" envir set in eval test 2:

var_i="var1" var_j="var2" var_by="var3" # test 1 works foo[eval1(var_i)==1 , sum(var2) , by=var3 ] # test 2 doesn't work foo[var1==1 , sum(eval1(var_j)) , by=var3] # test 3 works foo[var1==1 , sum(var2) , by=eval1(var_by)]

the j-exp, checks it's variables in environment of .sd, stands subset of data. .sd data.table holds columns that group.

when do:

foo[var1 == 1, sum(eval(parse(text=var_j))), by=var3]

directly, j-exp gets internally optimised/replaced sum(var2). sum(eval1(var_j)) doesn't optimised, , stays is.

then when gets evaluated each group, it'll have find var2, doesn't exist in parent.frame() function called, in .sd. example, let's this:

eval1 <- function(s) eval(parse(text=s), envir=parent.frame()) foo[var1 == 1, { var2 = 1l; eval1(var_j) }, by=var3] # var3 v1 # 1: e 1 # 2: c 1 # 3: 1 # 4: b 1 # 5: d 1

it find var2 it's parent frame. is, have point right environment evaluate in, additional argument value = .sd.

eval1 <- function(s, env) eval(parse(text=s), envir = env, enclos = parent.frame()) foo[var1 == 1, sum(eval1(var_j, .sd)), by=var3] # var3 v1 # 1: e 11.178035 # 2: c -12.236446 # 3: -8.984715 # 4: b -2.739386 # 5: d -1.159506

r data.table

Comments

Post a Comment

Popular posts from this blog

Delphi change the assembly code of a running process -

Delphi change the assembly code of a running process - i'm trying alter address 00741fa5 has push test.009e721c . alter push test.009e71c8 . procedure callback; asm force $9e71c8 end; procedure tform2.btn1click(sender: tobject); var ppid :dword; pprocess : cardinal; begin getwindowthreadprocessid(findwindow(nil,pchar('test')), @ppid); pprocess := openprocess(process_all_access, false, ppid); injectasm(pprocess, $741fa5, 10, integer(@callback), 0); end; here injectasm function (with error checking) function injectasm(process: longword; injectaddress, injectsize, codeaddress, codesize : integer): pointer; var csize, rsize : integer; replaced : array of byte; jmp : array [0..4] of byte; jmpaddress : integer; nopv : byte; : integer; nbr: ulong_ptr; begin //injectsize must equal or greater 5, because need space our //(far) jmp wwxxyyzz instruction //if there's no space, inject in place of few instructions if injectsize ...
Read more

json - Hibernate and Jackson (java.lang.IllegalStateException: Cannot call sendError() after the response has been committed) -

json - Hibernate and Jackson (java.lang.IllegalStateException: Cannot call sendError() after the response has been committed) - hello have problem hibernate , jackson. have 2 pojos @entity @table(name = "users") public class user implements serializable { static final long serialversionuid = 4235637833262722256l; @id @generatedvalue private int id; @column(name = "creation_date") private date creationdate; @column(name = "first_name") private string firstname; @column(name = "last_name") private string lastname; @version @column(name = "version") private int version; @column(name = "e_mail") private string email; @column(name = "enabled") private boolean enabled; @column(name = "login") private string login; @column(name = "password") private string password; @jsonmanagedreference("role") @onetomany(mappedby = "user", cascade = cascadetype.all,fetch = fetchtyp...
Read more

C++ 11 "class" keyword -

C++ 11 "class" keyword - i've started using c++ 11 little bit more , have few questions on special uses of class keyword. know it's used declare class, there's 2 instances have seen don't understand: method<class t>(); and class class_name *var; why precede typename keyword class in first example, , keyword pointer in sec example? that known elaborated type specifier , necessary when class name "shadowed" or "hidden" , need explicit. class t { }; // love of god don't t t; t t2; if compiler smart, give these warnings: main.cpp:15:5: error: must utilize 'class' tag refer type 't' in scope t t2; ^ class main.cpp:14:7: note: class 't' hidden non-type declaration of 't' here t t; ^ if class not defined, deed forwards declaration. for example: template <typename t> void method() { using type = typename t::value_type; } method...
Read more