Modifying Variable Length Strings in R

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In this article, we will explore how to modify variable length strings in R without reordering the vector. We will use a combination of string manipulation functions from the stringi library and R’s built-in indexing capabilities.

Problem Statement

The problem is that when modifying variable length strings, the positions within the vector are changed, leading to incorrect results. For example, in the given code, “C0200s” has moved from its original position to become “A1312s”.

Solution Overview

Our approach will be to use stri_split_boundaries to split the string into substrings separated by a specified type of delimiter (in this case, whitespace). We will then apply our modification logic to each substring and finally paste them back together to form the modified strings.

Step 1: Load Required Libraries

library(stringi)

Step 2: Define Input Strings

For demonstration purposes, let’s define a vector of input strings:

first <- c("A10", "A10r", "A1112", "A1112r", "A116", "A116r",
    "A1212", "A1212r", "A126", "A126r", "A1312", "A1312r",
    "A136", "A136r", "A20", "A20r", "A2112", "A2112r", "A216",
    "A216r", "A2212", "A2212r", "A226", "A226r", "A2312", "A2312r",
    "A236", "A236r", "A30", "A30r", "A3112", "A3112r")

Step 3: Apply Modification Logic

We will use lapply to apply our modification logic to each substring. Here’s the code:

unlist(lapply(stri_split_boundaries(first, type="character"), function(x) {

    if (length(x) < 3) {
        print(x)
        stop("Logic will not apply correctly")
    }

    # add an "s" to all strings not containing "r"
    if (tail(x, 1) != "r") x <- c(x, "s")

    if (length(x) < 4) {
        print(x)
        stop("Logic will not apply correctly")
    }

    # add a digit "0" after the first element, only if there were fewer than 5 elements
    if (length(x) < 5) x <- c(x[1], "0", x[-1])

    if (length(x) < 5) {
        print(x)
        stop("Logic will not apply correctly")
    }

    # adding a digit "0" after the third element, only if there were fewer than 6 elements
    if (length(x) < 6) x <- c(x[seq_len(3)], "0", x[-seq_len(3)])

    if (length(x) != 6) {
        print(x)
        stop("Check logic.")
    }

    paste(x, collapse="")
}))

Step 4: Execute Code

Finally, we execute the code using lapply:

modified_strings <- unlist(lapply(stri_split_boundaries(first, type="character"), function(x) {
    # ... (same modification logic as before)
}))

The modified strings are stored in the modified_strings vector.

Conclusion

In this article, we have demonstrated how to modify variable length strings in R without reordering the vector. We used a combination of string manipulation functions from the stringi library and R’s built-in indexing capabilities to achieve this result.

Note that this solution assumes that the input strings are whitespace-separated. If your input strings use a different type of delimiter, you may need to modify the code accordingly.

Also note that we applied sanity checks throughout the modification logic to ensure that our logic is robust and will not produce incorrect results for certain input values.

Last modified on 2024-09-16