[英]In R, how to restrict selection and setting of cell values of data.table to list of columns?
我需要將data.table的列子集中的所有“-1”實例設置為NA。
我可以將data.table中ALL列的所有此類實例設置為NA,如下所示:
dt <- data.table(c("-1","A","A","B"), c("A","B","-1","-1"),c("-1","B","B","-1") )
for (i in seq_along(dt))
set(dt, i=which(dt[[i]]=="-1"), j=i, value=NA)
> dt
V1 V2 V3
1: NA A NA
2: A B B
3: A NA B
4: B NA NA
但是如何將替換限制為列的子集,例如c(“V2”,“V3”)? 這不起作用:
dt <- data.table(c("-1","A","A","B"), c("A","B","-1","-1"),c("-1","B","B","-1") )
for (i in seq_along(dt[,c("V2","V3"),with=FALSE]))
set(dt[,c("V2","V3"),with=FALSE], i=which(dt[,c("V2","V3"),with=FALSE][[i]]=="-1"), j=i, value=NA)
dt
> dt
V1 V2 V3
1: -1 A -1
2: A B B
3: A -1 B
4: B -1 -1
我們可以循環遍歷名稱索引,並將這些列中-1的元素set
為NA。
for(j in paste0('V', 2:3)){
set(dt, i=which(dt[[j]]==-1), j=j, value=NA)
}
dt
# V1 V2 V3
#1: -1 A NA
#2: A B B
#3: A NA B
#4: B NA NA
編輯:根據@Frank的評論修改。
這是一種不使用for
循環的方法:
dt <- data.table(c("-1","A","A","B"), c("A","B","-1","-1"), c("-1","B","B","-1") )
dt$V2 = ifelse(dt$V2 == "-1", NA, dt$V2)
dt$V3 = ifelse(dt$V3 == "-1", NA, dt$V3)
dt
V1 V2 V3
1: -1 A NA
2: A B B
3: A NA B
4: B NA NA
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