通过引用在函数中添加大量列

本文介绍了通过引用在函数中添加大量列的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

在这种情况下，我无法弄清data.table的情况：

fooFun < tbl，totCols）{ tbl [，paste0（col，1：totCols）：= 0] }

从一个空的1-col数据表开始。

然后通过引用添加99列：

p>

> fooFun（tbl，99）> col1col1col1col1col2col1col2col3 col13col16col16col16col14col16col16 col27col38col29col28col29col30col31col32col35 col54col50col51col52col53col54col55col54col54 [57]col56col57col58col59col60col61col62col63col64col65col66 b $ b [71]col70col71col72col73col74col75col76col77 $ b [85]col84col85col86col87col88col89col90col91col92col93col94 b [99]col98col99

现在添加第100列：

> fooFun（tbl，100）> col1col1col1col1col2col1col2col3 col13col16col16col16col14col16col16 col27col38col29col28col29col30col31col32col35 col54col50col51col52col53col54col55col54col54 [57]col56col57col58col59col60col61col62col63col64col65col66 b $ b [71]col70col71col72col73col74col75col76col77 $ b [85]col84col85col86col87col88col89col90col91col92col93col94 b [99]col98col99

不存在...现在在函数调用之外添加一个列：

> tbl [，newCol：= 5] > col1col1col1col1col2col1col2col3 col13col16col16col16col14col16col16 col27col38col29col28col29col30col31col32col35 col54col50col51col52col53col54col55col54col54 [57]col56col57col58col59col60col61col62col63col64col65col66 b $ b [71]col70col71col72col73col74col75col76col77 $ b [85]col84col85col86col87col88col89col90col91col92col93col94 b [99]col98col99newCol

现在添加第100列：

> fooFun（tbl，100）> col1col1col1col1col2col1col2col3 col13col16col16col16col14col16col16 col27col38col29col28col29col30col31col32col35 col54col50col51col52col53col54col55col54col54 [57]col56col57col58col59col60col61col62col63col64col65col66 b $ b [71]col70col71col72col73col74col75col76col77 $ b [85]col84col85col86col87col88col89col90col91col92col93col94 b [99]col98col99newColcol100

现在再添加20个：

> fooFun（tbl，120）> col1col1col1col1col2col1col2col3 col13col16col16col16col14col16col16 col27col38col29col28col29col30col31col32col35 col54col50col51col52col53col54col55col54col54 [57]col56col57col58col59col60col61col62col63col64col65col66 b $ b [71]col70col71col72col73col74col75col76col77 $ b [85]col84col85col86col87col88col89col90col91col92col93col94 b [99]col98col99newColcol100col101col102col103col104col105col106col107col108 [113]col111col112col113col114col115col116col117col118col119col120

看起来OK。现在添加一堆：

> fooFun（tbl，240）> col1col1col1col1col2col1col2col3 col13col16col16col16col14col16col16 col27col38col29col28col29col30col31col32col35 col54col50col51col52col53col54col55col54col54 [57]col56col57col58col59col60col61col62col63col64col65col66 b $ b [71]col70col71col72col73col74col75col76col77 $ b [85]col84col85col86col87col88col89col90col91col92col93col94 b [99]col98col99newColcol100col101col102col103col104col105col106col107col108 col118col119col128col121col122col123col124 [col126]col112 127]col125col126col127col128col129col130col131col132col133col134col135col136col137col138 ]col139col140col141col142col143col144col145col146col147col148col149col150col151 col153col154col155col156col157col158col159col160col161col162col163col164col165col166 col167col168col169col170col171col172col173col174col175col176col177col178col179col180 col182col183col184col185col186col187col188col189col190col191col192col193 col196col197col198

发生了什么事？

解决方案

@Arun指出这个问题已在邮件列表中解决：＃5204 。按照该线程中的建议，我增加了在创建data.table时alloc_的列指针的默认数量：

options（datatable.alloccol = 900）

在已创建的表上增加列数超过100时分配100列。这可以解决在达到预分配限制时浅复制对象的基本问题，以便为此SO问题中的测试产生预期行为。

I can't figure out what's going on with data.table in this situation:

fooFun <- function(tbl, totCols) { tbl[, paste0("col", 1:totCols) := 0] }

Start with an empty 1-col data table.

> tbl = data.table(initialCol=double())

Then add 99 columns by reference:

> fooFun(tbl, 99) > colnames(tbl) [1] "initialCol" "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" "col10" "col11" "col12" "col13" [15] "col14" "col15" "col16" "col17" "col18" "col19" "col20" "col21" "col22" "col23" "col24" "col25" "col26" "col27" [29] "col28" "col29" "col30" "col31" "col32" "col33" "col34" "col35" "col36" "col37" "col38" "col39" "col40" "col41" [43] "col42" "col43" "col44" "col45" "col46" "col47" "col48" "col49" "col50" "col51" "col52" "col53" "col54" "col55" [57] "col56" "col57" "col58" "col59" "col60" "col61" "col62" "col63" "col64" "col65" "col66" "col67" "col68" "col69" [71] "col70" "col71" "col72" "col73" "col74" "col75" "col76" "col77" "col78" "col79" "col80" "col81" "col82" "col83" [85] "col84" "col85" "col86" "col87" "col88" "col89" "col90" "col91" "col92" "col93" "col94" "col95" "col96" "col97" [99] "col98" "col99"

All looks good. Now add the 100th column:

> fooFun(tbl, 100) > colnames(tbl) [1] "initialCol" "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" "col10" "col11" "col12" "col13" [15] "col14" "col15" "col16" "col17" "col18" "col19" "col20" "col21" "col22" "col23" "col24" "col25" "col26" "col27" [29] "col28" "col29" "col30" "col31" "col32" "col33" "col34" "col35" "col36" "col37" "col38" "col39" "col40" "col41" [43] "col42" "col43" "col44" "col45" "col46" "col47" "col48" "col49" "col50" "col51" "col52" "col53" "col54" "col55" [57] "col56" "col57" "col58" "col59" "col60" "col61" "col62" "col63" "col64" "col65" "col66" "col67" "col68" "col69" [71] "col70" "col71" "col72" "col73" "col74" "col75" "col76" "col77" "col78" "col79" "col80" "col81" "col82" "col83" [85] "col84" "col85" "col86" "col87" "col88" "col89" "col90" "col91" "col92" "col93" "col94" "col95" "col96" "col97" [99] "col98" "col99"

What? Not there... Now add one column outside of the function call:

> tbl[, newCol := 5] > colnames(tbl) [1] "initialCol" "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" "col10" "col11" "col12" "col13" [15] "col14" "col15" "col16" "col17" "col18" "col19" "col20" "col21" "col22" "col23" "col24" "col25" "col26" "col27" [29] "col28" "col29" "col30" "col31" "col32" "col33" "col34" "col35" "col36" "col37" "col38" "col39" "col40" "col41" [43] "col42" "col43" "col44" "col45" "col46" "col47" "col48" "col49" "col50" "col51" "col52" "col53" "col54" "col55" [57] "col56" "col57" "col58" "col59" "col60" "col61" "col62" "col63" "col64" "col65" "col66" "col67" "col68" "col69" [71] "col70" "col71" "col72" "col73" "col74" "col75" "col76" "col77" "col78" "col79" "col80" "col81" "col82" "col83" [85] "col84" "col85" "col86" "col87" "col88" "col89" "col90" "col91" "col92" "col93" "col94" "col95" "col96" "col97" [99] "col98" "col99" "newCol"

All good. Now add that 100th column:

> fooFun(tbl, 100) > colnames(tbl) [1] "initialCol" "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" "col10" "col11" "col12" "col13" [15] "col14" "col15" "col16" "col17" "col18" "col19" "col20" "col21" "col22" "col23" "col24" "col25" "col26" "col27" [29] "col28" "col29" "col30" "col31" "col32" "col33" "col34" "col35" "col36" "col37" "col38" "col39" "col40" "col41" [43] "col42" "col43" "col44" "col45" "col46" "col47" "col48" "col49" "col50" "col51" "col52" "col53" "col54" "col55" [57] "col56" "col57" "col58" "col59" "col60" "col61" "col62" "col63" "col64" "col65" "col66" "col67" "col68" "col69" [71] "col70" "col71" "col72" "col73" "col74" "col75" "col76" "col77" "col78" "col79" "col80" "col81" "col82" "col83" [85] "col84" "col85" "col86" "col87" "col88" "col89" "col90" "col91" "col92" "col93" "col94" "col95" "col96" "col97" [99] "col98" "col99" "newCol" "col100"

It's there now. Now add 20 more:

> fooFun(tbl, 120) > colnames(tbl) [1] "initialCol" "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" "col10" "col11" "col12" "col13" [15] "col14" "col15" "col16" "col17" "col18" "col19" "col20" "col21" "col22" "col23" "col24" "col25" "col26" "col27" [29] "col28" "col29" "col30" "col31" "col32" "col33" "col34" "col35" "col36" "col37" "col38" "col39" "col40" "col41" [43] "col42" "col43" "col44" "col45" "col46" "col47" "col48" "col49" "col50" "col51" "col52" "col53" "col54" "col55" [57] "col56" "col57" "col58" "col59" "col60" "col61" "col62" "col63" "col64" "col65" "col66" "col67" "col68" "col69" [71] "col70" "col71" "col72" "col73" "col74" "col75" "col76" "col77" "col78" "col79" "col80" "col81" "col82" "col83" [85] "col84" "col85" "col86" "col87" "col88" "col89" "col90" "col91" "col92" "col93" "col94" "col95" "col96" "col97" [99] "col98" "col99" "newCol" "col100" "col101" "col102" "col103" "col104" "col105" "col106" "col107" "col108" "col109" "col110" [113] "col111" "col112" "col113" "col114" "col115" "col116" "col117" "col118" "col119" "col120"

Looks OK. Now add a bunch more:

> fooFun(tbl, 240) > colnames(tbl) [1] "initialCol" "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" "col10" "col11" "col12" "col13" [15] "col14" "col15" "col16" "col17" "col18" "col19" "col20" "col21" "col22" "col23" "col24" "col25" "col26" "col27" [29] "col28" "col29" "col30" "col31" "col32" "col33" "col34" "col35" "col36" "col37" "col38" "col39" "col40" "col41" [43] "col42" "col43" "col44" "col45" "col46" "col47" "col48" "col49" "col50" "col51" "col52" "col53" "col54" "col55" [57] "col56" "col57" "col58" "col59" "col60" "col61" "col62" "col63" "col64" "col65" "col66" "col67" "col68" "col69" [71] "col70" "col71" "col72" "col73" "col74" "col75" "col76" "col77" "col78" "col79" "col80" "col81" "col82" "col83" [85] "col84" "col85" "col86" "col87" "col88" "col89" "col90" "col91" "col92" "col93" "col94" "col95" "col96" "col97" [99] "col98" "col99" "newCol" "col100" "col101" "col102" "col103" "col104" "col105" "col106" "col107" "col108" "col109" "col110" [113] "col111" "col112" "col113" "col114" "col115" "col116" "col117" "col118" "col119" "col120" "col121" "col122" "col123" "col124" [127] "col125" "col126" "col127" "col128" "col129" "col130" "col131" "col132" "col133" "col134" "col135" "col136" "col137" "col138" [141] "col139" "col140" "col141" "col142" "col143" "col144" "col145" "col146" "col147" "col148" "col149" "col150" "col151" "col152" [155] "col153" "col154" "col155" "col156" "col157" "col158" "col159" "col160" "col161" "col162" "col163" "col164" "col165" "col166" [169] "col167" "col168" "col169" "col170" "col171" "col172" "col173" "col174" "col175" "col176" "col177" "col178" "col179" "col180" [183] "col181" "col182" "col183" "col184" "col185" "col186" "col187" "col188" "col189" "col190" "col191" "col192" "col193" "col194" [197] "col195" "col196" "col197" "col198"

No good.

What's going on?

解决方案

@Arun pointed out that this issue has already been addressed on the mailing list: #5204. Following the advice in that thread, I increased the default number of column pointers that are alloc'd when a data.table is created:

options(datatable.alloccol = 900)

This way it won't hit the default pre-allocation of 100 columns when increasing the number of columns over 100 on an already-created table. This works around the underlying issue about shallow copying the object when the pre-allocation limit is reached, so that it produces the expected behavior for the tests in this SO question.