背景

Question

背景

该函数有一个简单的任务，即遍历因子元素，然后尝试将每个元素转换为double，integer，最后将其保留为字符。在每次计数时，相应的计数器增加。在末尾返回与最大计数器对应的字符串。

理性

这主要是一个学习示例。我遇到了一个凌乱的data.frame，其中包含一些我想使用的数据作为要素保存。变量实际上是双精度，整数或字符串。我想把它们带到那些类型。有一些更好的方法可以在基数R中完成，但是这个问题似乎是学习更多rcpp的好机会。

代码

#include <Rcpp.h>

// [[Rcpp::plugins(cpp11)]]

//' @title Guess Vector Type
//'
//' @description Function analyses content of a factor vector and attempts to
//'   guess the correct type.
//'
//' @param x A vector of factor class.
//'
//' @return A scalar string with class name.
//'
//' @export
//'
// [[Rcpp::export]]
Rcpp::String guess_vector_type(Rcpp::IntegerVector x) {

    // Define counters for all types
    int num_doubles = 0;
    int num_integers = 0;
    int num_strings = 0;

    // Converted strings
    double converted_double;
    int converted_integer;


    // Get character vector with levels
    Rcpp::StringVector levels = x.attr("levels");
    // Get integer vector with values
    // Rcpp::String type = x.sexp_type();
    // Returns integer vector type
    // Use iterator: https://teuder.github.io/rcpp4everyone_en/280_iterator.html
    for(Rcpp::IntegerVector::iterator it = x.begin(); it != x.end(); ++it) {
        // Get [] for vector element
        int index = std::distance(x.begin(), it);
        // Get value of a specific vector element
        int element = x[index];
        // Convert to normal string
        std::string temp = Rcpp::as<std::string>(levels[element]);
        // Try converting to an integer
        try
        {
            converted_integer = std::stoi(temp);
        }
        catch(...)
        {
            // Try converting to a doubke
            try
            {
                // Convert to ineteges
                converted_double = std::stod(temp);
            }
            catch(...)
            {
                ++num_integers;
            }
            ++num_doubles;
        }
        ++num_strings;

    }

    // Get max value of three variables
    // https://stackoverflow.com/a/2233412/1655567
    int max_val;
    max_val = num_doubles > num_integers? (num_doubles > num_strings? num_doubles: num_strings): (num_integers > num_strings? num_integers: num_strings);

    // Create results storage
    Rcpp::String res;


    // Check which value is matching max val
    if (max_val == num_doubles) {
        // Most converted to doubles
        res = "double";

    } else if (max_val == num_integers) {
        res = "integer";
    } else {
        res = "character";
    }

    // Return results vector
    return res;
}

测试

test_factor <- as.factor(rep(letters, 3))

应返回标量字符串"character"。

错误

guess_vector_type(test_factor)

 *** caught segfault ***
address 0xe1000013, cause 'memory not mapped'

我知道这与问题discussed here类似，但我不清楚错误在哪里。

更新

在评论之后，我更新了功能：

Rcpp::String guess_vector_type(Rcpp::IntegerVector x) {

    // Define counters for all types
    int num_doubles = 0;
    int num_integers = 0;
    int num_strings = 0;

    // Converted strings
    double converted_double;

    // flag for runnig more tests
    bool is_number;

    // Get character vector with levels
    Rcpp::StringVector levels = x.attr("levels");
    // Get integer vector with values
    // Rcpp::String type = x.sexp_type();
    // Returns integer vector type
    // Use iterator: https://teuder.github.io/rcpp4everyone_en/280_iterator.html
    for(Rcpp::IntegerVector::iterator it = x.begin(); it != x.end(); ++it) {
        // Get [] for vector element
        int index = std::distance(x.begin(), it);
        // Get value of a specific vector element
        int element = x[index];
        // Convert to normal string
        std::string temp = Rcpp::as<std::string>(levels[element - 1]);

        // Reset number checking flag
        is_number = 1;

        // Attempt conversion to double
        try {
            converted_double = std::stod(temp);
            } catch(...) {
                // Conversion failed, increase string count
                ++num_strings;
                // Do not run more test
                is_number = 0;
            }

        // If number run more tests
        if (is_number == 1) {
            // Check if converted string is an integer
            if(floor(converted_double) == converted_double) {
                // Increase counter for integer
                ++num_integers;
            } else {
                // Increase count for doubles
                ++num_doubles;
            }
        }
    }

    // Get max value of three variables
    // https://stackoverflow.com/a/2233412/1655567
    int max_val;
    max_val = num_doubles > num_integers? (num_doubles > num_strings? num_doubles: num_strings): (num_integers > num_strings? num_integers: num_strings);

    // Create results storage
    Rcpp::String res;


    // Check which value is matching max val
    if (max_val == num_doubles) {
        // Most converted to doubles
        res = "double";

    } else if (max_val == num_integers) {
        res = "integer";
    } else {
        res = "character";
    }

    // Return results vector
    return res;
}

测验

>> guess_vector_type(x = as.factor(letters))
[1] "character"
>> guess_vector_type(as.factor(1:10))
[1] "integer"
>> guess_vector_type(as.factor(runif(n = 1e3)))
[1] "double"

Answer 1

导致您的段错误的问题在于此行

std::string temp = Rcpp::as<std::string>(levels[element]);

由于R是1索引的，所以您需要

std::string temp = Rcpp::as<std::string>(levels[element - 1]);

但是，我还注意到，您在错误的位置增加了计数器（您需要在最里面的catch中增加字符串，并在catchs之外增加整数），并且需要在增量之后继续执行语句（否则，您最终还会进行不适用的增量）到您要执行的操作）。修复这些问题后，代码将按预期在测试用例上运行（但请参阅最后有关双精度和整数的更新）。

guess_vector_type(test_factor)
# [1] "character"

完整的工作代码是

#include <Rcpp.h>

// [[Rcpp::plugins(cpp11)]]

//' @title Guess Vector Type
//'
//' @description Function analyses content of a factor vector and attempts to
//'   guess the correct type.
//'
//' @param x A vector of factor class.
//'
//' @return A scalar string with class name.
//'
//' @export
//'
// [[Rcpp::export]]
Rcpp::String guess_vector_type(Rcpp::IntegerVector x) {

    // Define counters for all types
    int num_doubles = 0;
    int num_integers = 0;
    int num_strings = 0;

    // Converted strings
    double converted_double;
    int converted_integer;


    // Get character vector with levels
    Rcpp::StringVector levels = x.attr("levels");
    // Get integer vector with values
    // Rcpp::String type = x.sexp_type();
    // Returns integer vector type
    // Use iterator: https://teuder.github.io/rcpp4everyone_en/280_iterator.html
    for(Rcpp::IntegerVector::iterator it = x.begin(); it != x.end(); ++it) {
        // Get [] for vector element
        int index = std::distance(x.begin(), it);
        // Get value of a specific vector element
        int element = x[index];
        // Convert to normal string
        std::string temp = Rcpp::as<std::string>(levels[element - 1]);
        // Try converting to an integer
        try
        {
            converted_integer = std::stoi(temp);
        }
        catch(...)
        {
            // Try converting to a doubke
            try
            {
                // Convert to ineteges
                converted_double = std::stod(temp);
            }
            catch(...)
            {
                ++num_strings;
                continue;
            }
            ++num_doubles;
            continue;
        }
        ++num_integers;
    }

    // Get max value of three variables
    // https://stackoverflow.com/a/2233412/1655567
    int max_val;
    max_val = num_doubles > num_integers? (num_doubles > num_strings? num_doubles: num_strings): (num_integers > num_strings? num_integers: num_strings);

    // Create results storage
    Rcpp::String res;


    // Check which value is matching max val
    if (max_val == num_doubles) {
        // Most converted to doubles
        res = "double";

    } else if (max_val == num_integers) {
        res = "integer";
    } else {
        res = "character";
    }

    // Return results vector
    return res;
}

更新

我在其他一些示例上进行了尝试，发现它不能如预期的那样工作于double，因为该程序能够将“ 42.18”转换为整数（例如）。但是，它确实可以清晰地区分整数/双精度和字符：

test_factor <- as.factor(rep(letters, 3))
guess_vector_type(test_factor)
# [1] "character"

test_factor <- as.factor(1:3)
guess_vector_type(test_factor)
# [1] "integer"

test_factor <- as.factor(c(letters, 1))
guess_vector_type(test_factor)
# [1] "character"

test_factor <- as.factor(c(1.234, 42.1138, "a"))
guess_vector_type(test_factor)
# [1] "integer"

无论如何，这是与问题中提出的问题完全不同的问题，例如，您可能要咨询this Stack Overflow post。

简单的Rcpp函数，尝试捕获返回“未映射内存”错误

背景

理性

代码

测试

错误

更新

1 个答案:

更新