获取值的运行的开始和结束索引

Question

我有一个矢量:

a <- c(1, 1, 0, 0, 1, 2, 0, 0)

我想得到每次运行相等值的开始和结束索引:

number start  end
0        3     4
0        7     8
1        1     2
1        5     5
2        6     6

Answer 1

来自基地R的解决方案

a <- c(1,1,0,0,1,2,0,0)

# Get run length encoding
b <- rle(a)

# Create a data frame
dt <- data.frame(number = b$values, lengths = b$lengths)
# Get the end
dt$end <- cumsum(dt$lengths)
# Get the start
dt$start <- dt$end - dt$lengths + 1

# Select columns
dt <- dt[, c("number", "start", "end")]
# Sort rows
dt <- dt[order(dt$number), ]

dt
#  number start end
#2      0     3   4
#5      0     7   8
#1      1     1   2
#3      1     5   5
#4      2     6   6

更新

这是一个with使代码更简洁的解决方案.

with(rle(a), data.frame(number = values,
                        start = cumsum(lengths) - lengths + 1,
                        end = cumsum(lengths))[order(values),])
#  number start end
#2      0     3   4
#5      0     7   8
#1      1     1   2
#3      1     5   5
#4      2     6   6