r - Can I programmatically update the type of a set of columns (to factors) in data.table? -

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I would like to modify a set of columns within a data, which is the factor. If I knew the names of the columns in advance, then I think it would be straightforward. 

  Library (DataWabel) DT1 & lt; - data.table (a = (1: 4), b = representative (c ('a', 'b')), c = rep (c (0,1)) dt1 [, class (b)] dt1 [, B: = factor (b)] dt1 [, class (b)]   
 but I'm not, and instead there is a list of variable names  
 < Code> vars.factors & lt; - C ('B', 'C')   
 I can apply factor function to them without a problem ...  
  lapply (vars .factors, function x) get DT1 [, class (obtained (x)]) lapli (warfactor, function (x) dt1 [, factor (x)) lapply (wars. Factors, function (x ) DT1 [, Factor   
 But I do not know how to reassign or update the original column in the data table.  
 This fails. (X): in # get (x) Error: Invalid first argument  
  lapply (vars.factors, function (x) dt1 [, x: = factor (get (x))]) # code>  
 It is not ...  
  Lapli (warfactor, function (x) dt1 [, get (x): = factor (get (x))] # in error (x) : Object 'B' was not found   
 NB I tried the proposed answer without any luck.   
 
 
 Yes, it is quite straightforward:    D. 1 [, (vars.factors): = lapali (SD, AEFactor), SDCL = WARS .factors]   
  LHS  (of: = in  j ), we specify the names of the columns. If a column already exists, it will be updated, otherwise, a new column will be created. In RHS, we have . Loops on all the columns in the SD (which stands for  D  at  S ), and we call it the  sd  Should be with the  .ccols  argument.  
 Comment later on:  
 Note that we should wrap LHS with  ()  for  Assessment  and  Find the names of the columns within the vars.factors variable. The reason is that we allow syntax.  
  DT [, call: = value]  < / Pre> 
 When specifying the column name, there is only one column to specify that for pure convenience (without quotes) a symbol is called a  call  And assigns it to  value   
 To separate both of these cases, we need  ()   ()  is enough to wrap it so that we can actually get value within the variable.

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