通过动态列名子集化数据表 [英] subsetting data tables by dynamic column names
问题描述
我尝试使用动态列名称子表,但无法获得以下语句。
I'm trying to subset a table using dynamic column names, but cannot get the following statement to work
mm2myModuleByYear[grep(i,colnames(mm2myModuleByYear),value=TRUE)==mId,authId]
以下示例数据
i<-1997
mId<-37
mm2myModuleByYear<-structure(list(authId = c(220, 2269, 2270, 2271, 2991, 2992),
module1994 = c(NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_), module1995 = c(NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_), module1996 = c(NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_
), module1997 = c(1428L, 669L, 37L, NA, NA, NA), module1998 = c(1428L,
669L, 37L, NA, 832L, 832L), module1999 = c(1428L, 669L, 37L,
NA, 832L, 832L), module2000 = c(31L, 136L, 8L, NA, 1046L,
1046L), module2001 = c(31L, 136L, 8L, NA, 1046L, 1046L),
module2002 = c(31L, 136L, 8L, NA, 1046L, 1046L), module2003 = c(31L,
136L, 8L, 2314L, 1046L, 1046L), module2004 = c(955L, 320L,
10L, 1791L, 1361L, 1361L), module2005 = c(955L, 320L, 10L,
1791L, 1361L, 1361L), module2006 = c(955L, 320L, 10L, 1791L,
1361L, 1361L), module2007 = c(955L, 320L, 10L, 1791L, 1361L,
1361L), module2008 = c(955L, 320L, 10L, 1791L, 1361L, 1361L
), module2009 = c(16L, 374L, 11L, 1960L, 1544L, 1544L), module2010 = c(16L,
374L, 11L, 1960L, 1544L, 1544L), module2011 = c(16L, 374L,
11L, 1960L, 1544L, 1544L), module2012 = c(16L, 374L, 11L,
1960L, 1544L, 1544L), module2013 = c(16L, 374L, 11L, 1960L,
1544L, 1544L)), .Names = c("authId", "module1994", "module1995",
"module1996", "module1997", "module1998", "module1999", "module2000",
"module2001", "module2002", "module2003", "module2004", "module2005",
"module2006", "module2007", "module2008", "module2009", "module2010",
"module2011", "module2012", "module2013"), sorted = "module1996", class = c("data.table",
"data.frame"), row.names = c(NA, -6L), .internal.selfref = <pointer: 0x2697d88>)
但是,如果我做的事情有所不同,例如
However, if I do something vary similar, like
mm2myModuleByYear[module1997==mId,grep(i,colnames(mm2myModuleByYear)),with=FALSE]
这样工作。我做错了什么?我们如何有条件地设置数据表中的子列?
This works. Am I doing something incorrectly? How do I conditionally set the subset column in a data table?
推荐答案
i :
Let's look at your expression in i
:
grep(i,colnames(mm2myModuleByYear),value=TRUE)
[1] "module1997"
因此表达式:
grep(i,colnames(mm2myModuleByYear),value=TRUE)==mId
# [1] FALSE
会返回 FALSE
(当然是module1997!= 37)。你打算在这里获取由 grep()
表达式返回的列。为此,您可以使用基本R中的 get()
。
would return FALSE
(of course "module1997" != 37). What you intend here is to fetch the column returned by your grep()
expression. To to that, you can use get()
from base R.
with(mm2myModuleByYear, get(grep(i,colnames(mm2myModuleByYear),value=TRUE)))
# [1] 1428 669 37 NA NA NA
简而言之,您的i表达式中缺少 get()
。
In short, you're missing a get()
in your i-expression.
mm2myModuleByYear[get(grep(i,colnames(mm2myModuleByYear),value=TRUE))==mId, authId]
# [1] 2270
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