如何使用R索引主题 [英] How to Index subjects using R

问题描述

我在R工作，我有一个数据集，每个主题有多个条目。我想创建一个索引变量，按主题索引。例如：

I am working in R and I have a Data set that has multiple entries for each subject. I want to create an index variable that indexes by subject. For example:

    Subject Index
1       A     1
2       A     2
3       B     1
4       C     1
5       C     2
6       C     3
7       D     1
8       D     2
9       E     1

第一个A条目索引为1，而第二个A条目索引为2.第一个B条目索引为1，等等。

The first A entry is indexed as 1, while the second A entry is indexed as 2. The first B entry is indexed as 1, etc.

任何帮助都会非常棒！

推荐答案

Here.sa快速 data.table aproach

Here.s a quick data.table aproach

library(data.table)
setDT(df)[, Index := seq_len(.N), by = Subject][]
#    Subject Index
# 1:       A     1
# 2:       A     2
# 3:       B     1
# 4:       C     1
# 5:       C     2
# 6:       C     3
# 7:       D     1
# 8:       D     2
# 9:       E     1

或者基数R

with(df, ave(as.numeric(Subject), Subject, FUN = seq_along))
## [1] 1 2 1 1 2 3 1 2 1

或者使用 dplyr （不要在 data.table 类上运行）

Or with dplyr (don't run this on a data.table class)

library(dplyr)
df %>%
  group_by(Subject) %>%
  mutate(Index = row_number())

这篇关于如何使用R索引主题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！