Concatenate a vector of strings/character

Concatenating Vectors of Strings in R

Learn various methods to effectively combine vectors of strings or characters in R, from basic functions to advanced techniques for complex scenarios.

In R, concatenating strings or character vectors is a common task in data manipulation and text processing. Whether you need to join elements of a single vector, combine multiple vectors, or build complex strings from various components, R provides several powerful and flexible functions to achieve this. This article will explore the most frequently used methods, their nuances, and best practices.

Basic String Concatenation with paste() and paste0()

The paste() and paste0() functions are the workhorses for string concatenation in R. They are highly versatile and can handle various input types, automatically converting non-character arguments to character strings before joining them. The primary difference lies in their default separator:

• paste(): Uses a space (" ") as the default separator between concatenated elements.
• paste0(): Uses an empty string ("") as the default separator, meaning elements are joined directly without any space in between.

vec1 <- c("Hello", "World")
vec2 <- c("R", "Programming")

# Using paste() with default separator
paste(vec1, vec2)
# Output: [1] "Hello R" "World Programming"

# Using paste0() with no separator
paste0(vec1, vec2)
# Output: [1] "HelloR" "WorldProgramming"

# Custom separator with paste()
paste(vec1, vec2, sep = "-")
# Output: [1] "Hello-R" "World-Programming"

# Concatenating elements within a single vector
paste(vec1, collapse = ", ")
# Output: [1] "Hello, World"

paste0(vec1, collapse = "")
# Output: [1] "HelloWorld"

Examples of paste() and paste0() for vector concatenation.

Understanding collapse vs. sep

It's crucial to distinguish between the sep and collapse arguments in paste() and paste0():

• sep: Defines the separator between individual arguments passed to paste() or paste0(). This applies element-wise if multiple vectors are provided.
• collapse: Defines the separator used to collapse the resulting vector of strings into a single, long string. This argument is applied after any sep operations have occurred.

flowchart TD
    A["Input Vectors (e.g., vec1, vec2)"] --> B{"Apply `sep` (element-wise)"}
    B --> C["Intermediate Vector of Strings"]
    C --> D{"Apply `collapse` (to single string)"}
    D --> E["Final Single String Output"]
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style E fill:#bbf,stroke:#333,stroke-width:2px

Flowchart illustrating the order of sep and collapse operations in paste().

Advanced Concatenation with stringr::str_c()

For users who prefer a more consistent and pipe-friendly syntax, the stringr package (part of the tidyverse) offers str_c(). This function is similar to paste0() but provides a slightly different interface and often integrates better into data manipulation pipelines.

str_c() defaults to no separator, just like paste0(), but also offers sep and collapse arguments for fine-grained control.

library(stringr)

vec1 <- c("Alpha", "Beta")
vec2 <- c("One", "Two")

# Basic concatenation (like paste0())
str_c(vec1, vec2)
# Output: [1] "AlphaOne" "BetaTwo"

# With a separator
str_c(vec1, vec2, sep = "_")
# Output: [1] "Alpha_One" "Beta_Two"

# Collapsing into a single string
str_c(vec1, vec2, sep = "-", collapse = "; ")
# Output: [1] "Alpha-One; Beta-Two"

# Concatenating a single vector with collapse
str_c(vec1, collapse = ", ")
# Output: [1] "Alpha, Beta"

Using stringr::str_c() for string concatenation.