在使用模式融化后,将"变量"列的数字表示转换为原始字符串

我使用patterns()参数data.table::melt()来融合具有几个容易定义的模式的列的数据.它正在工作,但我没有看到我如何创建一个字符索引变量而不是默认的数字细分.

例如,在A中,dog和cat列已编号...请查看"变量"列:

A = data.table(idcol = c(1:5),
            dog_1 = c(1:5),   cat_1 = c(101:105),
            dog_2 = c(6:10),  cat_2 = c(106:110),
            dog_3 = c(11:15), cat_3 = c(111:115))   
head(melt(A, measure = patterns("^dog", "^cat"), value.name = c("dog", "cat")))

   idcol variable dog cat
1:     1        1   1 101
2:     2        1   2 102
3:     3        1   3 103
4:     4        1   4 104
5:     5        1   5 105
6:     1        2   6 106

但是,在B中,dog和cat列用文本编号,但"变量"列仍然是数字.

B = data.table(idcol = c(1:5),
                dog_one = c(1:5),     cat_one = c(101:105),
                dog_two = c(6:10),    cat_two = c(106:110),
                dog_three = c(11:15), cat_three = c(111:115))
head(melt(B, measure = patterns("^dog", "^cat"), value.name = c("dog", "cat")))

   idcol variable dog cat
1:     1        1   1 101
2:     2        1   2 102
3:     3        1   3 103
4:     4        1   4 104
5:     5        1   5 105
6:     1        2   6 106

如何用一个/两个/三个而不是1/2/3填充"变量"列？

可能有更简单的方法,但这似乎有效:

# grab suffixes of 'variable' names
suff <- unique(sub('^.*_', '', names(B[ , -1])))
# suff <- unique(tstrsplit(names(B[, -1]), "_")[[2]])

# melt
B2 <- melt(B, measure = patterns("^dog", "^cat"), value.name = c("dog", "cat"))

# replace factor levels in 'variable' with the suffixes
setattr(B2$variable, "levels", suff)

B2
#     idcol variable dog cat
# 1:      1      one   1 101
# 2:      2      one   2 102
# 3:      3      one   3 103
# 4:      4      one   4 104
# 5:      5      one   5 105
# 6:      1      two   6 106
# 7:      2      two   7 107
# 8:      3      two   8 108
# 9:      4      two   9 109
# 10:     5      two  10 110
# 11:     1    three  11 111
# 12:     2    three  12 112
# 13:     3    three  13 113
# 14:     4    three  14 114
# 15:     5    three  15 115

请注意,在此主题上存在一个未解决的问题,其他一些替代方案:FR:扩展用于处理输出名称的熔解功能.

这是我认为good'ol data.table更清洁的(罕见)情况之一.它的variable参数在这里派上用场了 - 'value'列的名称和'variable'列的级别都是一次性生成的:

reshape(data = B,
        varying = names(B[ , -1]),
        sep = "_",
        direction = "long")