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POData.table assign value to existing column
 

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  1. POData.table assign value to existing column
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    <p>I am performing an apparently simple assignment in a data.table object.</p> <pre><code>library(RODBC) library(data.table) library(ffbase) library(plyr) library(doBy) library(reshape2) ST_a = Sys.Date()-7 ST = paste("'",as.character(format(ST_a,"%d.%m.%Y")),"'",sep="") rd_a = Sys.Date()- 41 rd = paste("'",as.character(format(rd_a,"%d.%m.%Y")),"'",sep="") ch&lt;-odbcConnect("db",uid="user",pwd="psw") chunks &lt;- c(seq.Date(from=rd_a, to=ST_a, by = 20),ST_a) started.at &lt;- proc.time() Sys.sleep(1) memory.limit(size=4095) for (i in 1:(length(chunks)-1)){ start &lt;- paste("'",as.character(format(chunks[i],"%d.%m.%Y")),"'",sep="") end &lt;- paste("'",as.character(format(chunks[i+1],"%d.%m.%Y")),"'",sep="") query &lt;- paste("Select * from DATA_LOCAL_V where id='EHPFCMO' and timestamp&gt;",rd," and reference_date&gt;=",start," and reference_date&lt;",end,sep="") EHPFC.ck &lt;- data.table(sqlQuery(ch,query,stringsAsFactors=FALSE)) EHPFC.ck[,TIMESTAMP:=TIMESTAMP-60^2] EHPFC.ck[, pod:=7] EHPFC.ck[as.POSIXlt(EHPFC.ck$TIMESTAMP)$hour %in% c(20:23), pod:=23] EHPFC.ck[as.POSIXlt(EHPFC.ck$TIMESTAMP)$hour %in% c(8:19), pod:=19] EHPFC.ck[,day:=as.Date(trunc(TIMESTAMP))] EHPFC.ck[,TIMESTAMP:=NULL] EHPFC.ck &lt;- EHPFC.ck[,mean(VALUE),by=list(ID,REFERENCE_DATE,day,pod)] setnames(EHPFC.ck,"V1","price") EHPFC.ck &lt;- as.ffdf(EHPFC.ck) if (i==1){ EHPFC &lt;- EHPFC.ck } else { EHPFC &lt;- ffdfappend(EHPFC,EHPFC.ck[,]) } rm(EHPFC.ck) gc() } EHPFC &lt;- data.table(EHPFC[,]) EHPFC &lt;- orderBy(~day+pod+REFERENCE_DATE, data=EHPFC) a &lt;- c(0,log(EHPFC[-1,price]/EHPFC[-nrow(EHPFC),price])) EHPFC &lt;- EHPFC[,RoR:=a] </code></pre> <p>By doing that I get the following error msg:</p> <pre><code>error in `[.data.table`(EHPFC, , `:=`(RoR, a)) : At an earlier point, this data.table has been copied by R. Avoid key&lt;-, names&lt;- and attr&lt;- which in R currently (and oddly) all copy the whole data.table. Use set* syntax instead to avoid copying: setkey(), setnames() and setattr(). If this message doesn't help, please ask on datatable-help. </code></pre> <p>The object EHPFC looks like the following:</p> <pre><code>EHPFC ID REFERENCE_DATE day pod price RoR [1,] EHPFCMO 2012-10-27 2012-10-27 7 35.34625 0 [2,] EHPFCMO 2012-10-28 2012-10-27 7 35.34625 0 [3,] EHPFCMO 2012-10-29 2012-10-27 7 35.34625 0 [4,] EHPFCMO 2012-10-30 2012-10-27 7 35.34625 0 [5,] EHPFCMO 2012-10-31 2012-10-27 7 35.34625 0 </code></pre> <p>I am a bit confused why this is happening.</p> <p>Any idea? Thanks in advance.</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USddg
    1. USddg
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. COHard to say without more information. Have you done any of the no-nos mentioned in the error?
      singulars
      1. POData.table assign value to existing column
      1. USRoland
    2. COAnd it's the "and in various steps modified" bit that we need more information about.
      singulars
      1. POData.table assign value to existing column
      1. USMatt Dowle
    3. COHi, Thanks for your feedback. I copied the full code I am running in the question. To give you some background, I am working with a very large data set (etwas 75Mio. rows). Hence to avoid the usual memory issues I am partitioning the data in chuncks. I do a few steps on every chunck and I use a ff object to temporarely store the results. When I am ready I transform the ff object back in a data.table object. Thanks in advance for your suggestions
      singulars
      1. POData.table assign value to existing column
      1. USddg
 

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