数据条件表的最大分组条件

本文介绍了数据条件表的最大分组条件的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我有这样的数据:

library(data.table) group <- c("a","a","a","b","b","b") cond <- c("N","Y","N","Y","Y","N") value <- c(2,1,3,4,2,5) dt <- data.table(group, cond, value) group cond value a N 2 a Y 1 a N 3 b Y 4 b Y 2 b N 5

当整个组的cond为Y时，我想返回最大值.像这样:

I would like to return max value when the cond is Y for the entire group. Something like this:

group cond value max a N 2 1 a Y 1 1 a N 3 1 b Y 4 4 b Y 2 4 b N 5 4

我尝试将ifelse条件添加到分组的max中，但是，当行不符合条件时，我最终只是返回NA的no条件:

I've tried adding an ifelse condition to a grouped max, however, I end up just returning the no condition of NA when the row doesn't meet the condition:

dt[, max := ifelse(cond=="Y", max(value), NA), by = group]

推荐答案

假定对于每个组"，我们需要获取值"的 max ，其中"cond"为"Y"，按组"分组后，将值"与逻辑条件( cond =='Y')进行子集并获得 max 值

Assuming that for each 'group' we need to get the max of 'value' where the 'cond' is "Y", after grouping by 'group', subset the 'value' with the logical condition (cond == 'Y') and get the max value

dt[, max := max(value[cond == 'Y']), by = group] dt # group cond value max #1: a N 2 1 #2: a Y 1 1 #3: a N 3 1 #4: b Y 4 4 #5: b Y 2 4 #6: b N 5 4