我通过ODBC从SQL数据库中提取了一些数据,并且列被自动设置为factor
。它看起来像下面这样:
library(RODBC)
library(data.table)
data <- data.table(sqlQuery(channel, query))
我的数据看起来像这样,只是有更多的列:
data <- data.table("C1"=as.factor(c(letters[1:4], "NULL", letters[5])),
"C2"=as.factor(c(rnorm(3), "NULL", rnorm(2))),
"C3"=as.factor(c(letters[1], "NULL", letters[2:4], "NULL")))
> data
C1 C2 C3
1: a -0.190200079604691 a
2: b 0.310548914832963 NULL
3: c 0.0153099116493453 b
4: d NULL c
5: NULL 0.157187027626419 d
6: e 0.118537540781528 NULL
> str(data)
Classes ‘data.table’ and 'data.frame': 6 obs. of 3 variables:
$ C1: Factor w/ 6 levels "a","b","c","d",..: 1 2 3 4 6 5
$ C2: Factor w/ 6 levels "-0.190200079604691",..: 1 5 2 6 4 3
$ C3: Factor w/ 5 levels "a","b","c","d",..: 1 5 2 3 4 5
- attr(*, ".internal.selfref")=<externalptr>
我该如何将 "NULL" 替换为 NA
?在这里,我希望 R
将这些 SQL "NULL" 字符串视为缺失值 NA
。我尝试了以下方法,但似乎 NA
会导致问题。
for (col in names(data)) {
set(data, which(data[[col]]=="NULL"), col, NA)
}
> Error in set(data, which(data[[col]] == "NULL"), col, NA) :
Can't assign to column 'C1' (type 'factor') a value of type 'logical' (not character, factor, integer or numeric)
RODBC解决方案
感谢@user20650的建议,您可以通过执行data <- data.table(sqlQuery(channel, query, na.strings=c("NA", "NULL")))
来控制sqlQuery
中的缺失值。然而,如果您的数据源格式不正确,仍有可能出现此问题,因此这不是该帖子的通用解决方案。
NULL
。 - IRTFMsqlQuery
中不使用na.strings = c("NA", "NULL")
或类似的方法,以便在读取时将值设置为缺失? - user20650