聚合数据框中的列

df1 <- read.table(text = "V1    V2
    21140 -2
    21140  0
    21140  2
    21140 -1
     3878  0
     3878  1
     3878  2
   20434  -1
   20434   2
   20434   1", header = TRUE)

for getting the mean i used the following command

为了获得平均值我使用了以下命令

sample.test.final <- df1[,list(V2 = mean(V2)), by = c("V1")] 

Now i want the following results

现在我想要以下结果

condition : if the value of V2 for corresponding V1 is negative select that value or else use the max positive value

条件:如果相应V1的V2值为负,则选择该值或使用最大正值

df2 <-      "V1    V2
            21140  -2
             3878   2
            20434  -1"

1 个解决方案

#1

Simply use if/else condition check to summarize the column:

只需使用if / else条件检查来汇总列:

df1[, .(V2 = if(all(V2 >= 0)) max(V2) else V2[V2 < 0]), V1]

#      V1 V2
#1: 21140 -2
#2: 21140 -1
#3:  3878  2
#4: 20434 -1

_{Note this keeps all negative values in V2 if there's any.}

注意,如果有的话,这会将所有负值保存在V2中。