整个周末这个问题困扰着我。我想根据另一列的组计算列中的' 1的数量。我想遍历许多列,我在这里给出的例子只是一个简单的例子。我认为DT1和DT2应该给我相同的结果,但显然DT1不起作用。谁能告诉我这是什么原因?谢谢!
DT <- data.table(Sample.name = c("A","B","C","A","A","B"),
Class1 = c(1, 0, 1, 0, 1, 0),
Class2 = c(1, 1, 1, 0, 1, 1))
round.test <- colnames(DT)
round.test <- round.test[c(2, 3)]
round.test <- noquote(round.test)
DT1 <- DT[, sum((round.test[1]) == 1),
by = Sample.name]
DT2 <- DT[, sum(Class1 == 1),
by = Sample.name]
答案 0 :(得分:1)
从列名称的字符向量开始,您可以使用get
来获取列值:
round.test <- colnames(DT)
round.test <- round.test[c(2, 3)]
DT[, sum(get(round.test[1]) == 1), .(Sample.name)]
# Sample.name V1
#1: A 2
#2: B 0
#3: C 1
DT[, lapply(round.test, function(col) sum(get(col) == 1)), .(Sample.name)]
# Sample.name V1 V2
#1: A 2 2
#2: B 0 2
#3: C 1 1
或者您可以使用.SDcols
传递列名,并通过.SD
访问列:
DT[, lapply(.SD, function(col) sum(col == 1)), by=.(Sample.name), .SDcols=round.test]
# Sample.name Class1 Class2
#1: A 2 2
#2: B 0 2
#3: C 1 1