R语言向量元素条件追加需求：无小数点元素合并处理

Alright, let's break down how to solve this problem: we have a character vector where we need to combine consecutive elements only if neither of them contains a decimal point. The merged element should use a dot as a separator, and we need to remove the second element once it's appended to the first.

First, let's confirm the original vector and expected output to make sure we're aligned:

• Original vector: a = c("135","00","85","6","0.00","6","0.00","0.00","85","61","0.00")
• Expected result: "135.00","85.6","0.00","6","0.00","0.00","85.61","0.00"

Simple Loop-Based Solution #

A loop is perfect here because we're modifying the vector as we iterate (we need to skip elements once they're merged). Here's the code that gets the job done:

# Define your original vector
a <- c("135","00","85","6","0.00","6","0.00","0.00","85","61","0.00")

# Start at the first element
i <- 1

# Loop until we reach the second-to-last element
while (i < length(a)) {
  # Check if current AND next element have no decimal points
  if (!grepl("\\.", a[i]) && !grepl("\\.", a[i+1])) {
    # Merge them with a dot
    a[i] <- paste0(a[i], ".", a[i+1])
    # Remove the now-redundant next element
    a <- a[- (i + 1)]
    # Don't increment i—since we just removed an element, the next candidate is still at i+1
  } else {
    # Move to the next element if no merge happened
    i <- i + 1
  }
}

# Check the result
print(a)

What this code does: #

• grepl("\\.", x) checks if a string has a decimal point. The ! flips it to check for strings without dots.
• When we find a pair to merge, we update the current element to be the combined string, then drop the second element. We don't increment i here because the element after the merged pair is now in the position we just checked—we need to verify if it should merge with the new current element.
• If no merge is needed, we just move to the next element.

Running this will output exactly what you want:

[1] "135.00" "85.6"   "0.00"   "6"      "0.00"   "0.00"   "85.61"  "0.00"

Optional Vectorized Approach (No Loops) #

If you prefer avoiding loops (maybe for larger vectors), you can use dplyr and tidyr to group and merge elements. This is a bit more abstract, but works just as well:

library(dplyr)
library(tidyr)

# Turn the vector into a data frame with helper columns
df <- tibble(
  value = a,
  position = seq_along(a),
  has_decimal = grepl("\\.", value)
)

# Create groups where consecutive non-decimal elements belong together
df <- df %>%
  mutate(merge_group = cumsum(has_decimal | lag(has_decimal, default = TRUE)))

# Merge within each group
final_vector <- df %>%
  group_by(merge_group) %>%
  summarise(
    value = ifelse(n() == 2 && all(!has_decimal), 
                   paste(value, collapse = "."), 
                   value)
  ) %>%
  ungroup() %>%
  pull(value)

print(final_vector)

This will also produce the expected result, though the loop version is more straightforward for this specific problem.

内容的提问来源于stack exchange，提问作者NinjaR