Extracting Trailing Zeroes from a String in R

Introduction

In this article, we will explore how to extract trailing zeroes from multiple parts of a string in R. We will use two approaches: one using sprintf and another using regular expressions.

Background

When working with strings in R, it is common to encounter data that requires formatting or manipulation. In this case, we are dealing with a specific type of string that consists of two parts separated by a dash (-). The first part contains digits, while the second part also contains a digit. Our goal is to add trailing zeroes to both parts of the string.

Approach 1: Using sprintf

The first approach uses the sprintf function, which allows us to format strings in R.

df1$v2[i1] <- sprintf('%s-%02d', sub('-.*', '', df1$v1[i1]), 
                        as.numeric(sub('.*-', '', df1$v1[i1])))

This code works by:

1. Extracting the part after the dash using sub('-.*', '', df1$v1[i1]).
2. Converting this extracted string to an integer using as.numeric(sub('.*-', '', df1$v1[i1])).
3. Adding leading zeroes using %02d, where 0 is the minimum number of digits required.
4. Replacing the original part with the formatted string.

Output

The resulting data frame will have trailing zeroes added to both parts of the string:

  #           v1          v2
#1  19956673-1 19956673-01
#2 20043747-23 20043747-23
#3  20056956-1 20056956-01
#4     36628-2    36628-02
#5     45820-4    45820-04
#6         478         478
#7         115         115

Approach 2: Using Regular Expressions

The second approach uses regular expressions to capture the digits from both parts of the string.

df1$v2 <- sub('^(\\d+)-(\\d)$', '\\1-0\\2', df1$v1)

This code works by:

1. Capturing one or more digits (\\d+) at the start of the string using ^.
2. Capturing a single digit at the end of the string using $.
3. Replacing the original string with the captured groups and a backreference to the first group followed by a dash, then the second group.

Data

We will use a sample data frame to demonstrate these approaches:

df1 <- structure(list(v1 = c("19956673-1", "20043747-23", "20056956-1", 
                            "36628-2", "45820-4", "478", "115")), row.names = c(NA, -7L), 
                      class = "data.frame")

This data frame has two columns: v1 and v2, where v1 contains the original strings and v2 is empty.

Conclusion

In this article, we explored how to extract trailing zeroes from multiple parts of a string in R using two approaches: one using sprintf and another using regular expressions. Both methods can be used depending on the specific requirements of your project.

Last modified on 2023-08-07