我正在尝试编写一个排序程序，试图对我拥有的数据集进行排序。排序的关键是Grid_ID，它恰好是字母数字数据。我试图据此进行排序
它给我一个错误
在进行调试时，代码的读取部分似乎起作用。将文件内容读入DataContainer数据将填充正确的键和文本位置数据。
但是当涉及到std::sort时，当程序“less”被调用时，const GridLabel＆elem2总是在第二次迭代后变为零或空。
以下是一些数据集和部分源代码(我不包括按排序顺序写内容，但应可运行)
感谢帮助!
这是部分数据集
Grid_Id,Speed,Acc,ID
K31,173,8.37,1
K29,143,3.36,2
K29,107,4.56,3
K30,133,5.97,4
K30,153,2.38,5
J27,203,1.86,6
J27,143,1.59,7
I26,73,7.66,8
I27,134,2.86,9
这是代码
#include <algorithm>
#include <functional>
#include <fstream>
#include <string>
#include <deque>
#include <vector>
#include <iostream>
#include <sstream>
struct GridLabel
{
std::string key_;
std::istream::pos_type pos_; // position in stream where this line starts
GridLabel( const std::string& key, const std::istream::pos_type& pos) : key_( key)
, pos_( pos)
{
}
const GridLabel& operator=( const GridLabel& other)
{
key_ = other.key_;
pos_ = other.pos_;
return *this;
}
};
typedef std::vector< GridLabel> DataContainer;
// Return whether first element is smaller than the second
bool less( const GridLabel& elem1, const GridLabel& elem2 )
{
std::stringstream ss1, ss2;
ss1 << elem1.key_.at(0);
ss2 << elem2.key_.at(0);
int value = (ss1.str()).compare(ss2.str());
if( value < 0 )
{
return true;
}
else if( value == 0)
{
// need to check if the rest are smaller
std::string substr1 = elem1.key_.substr(1, std::string::npos);
std::string substr2 = elem2.key_.substr(1, std::string::npos);
return (std::atoi(substr1.c_str()) < std::atoi(substr2.c_str()));
}
else
{
return false;
}
}
int main(int argc, char* argv[])
{
DataContainer data;
// read data into the vector here
std::ifstream input( "some_file.csv");
// check if it is correct
if ( !input.good())
{
std::cerr << "Input file can not be openned." << std::endl;
return -1;
}
std::string text;
std::string key;
std::istream::pos_type pos;
int count=0, save=0;
// to skip the header
std::getline( input, text);
for( int line = 0; !input.eof(); ++line)
{
// store the position before reading the line
pos = input.tellg();
std::getline( input, text);
// parse it
save = text.find(",");
key = text.substr(0,(save));
data.push_back( GridLabel( key, pos));
}
// sort the data in sorted order
std::sort( data.begin(), data.end(), less);
// create the new file
...............
return 0;
}
最佳答案
简化的less()进行比较
GridLabel::key的第一个字符GridLabel::key的第二个字符开始的整数。 这将不考虑
GridLabel::key中存储的其他内容。 (这可能是OP想要的。)样品:
#include <algorithm>
#include <iostream>
#include <string>
struct GridLabel {
std::string key;
};
bool less(const GridLabel &elem1, const GridLabel &elem2)
{
// compare first chars of keys
const char c1 = elem1.key.at(0), c2 = elem2.key.at(0);
if (c1 != c2) return c1 < c2;
// compare integral beginning in 2nd char of keys
const int i1 = atoi(elem1.key.c_str() + 1);
const int i2 = atoi(elem2.key.c_str() + 1);
return i1 < i2;
}
int main()
{
GridLabel data[] = {
{ "K31,173,8.37,1" },
{ "K29,143,3.36,2" },
{ "K29,107,4.56,3" },
{ "K30,133,5.97,4" },
{ "K30,153,2.38,5" },
{ "J27,203,1.86,6" },
{ "J27,143,1.59,7" },
{ "I26,73,7.66,8" },
{ "I27,134,2.86,9" }
};
{ std::cout << "Original data:\n";
int i = 0;
for (const GridLabel &entry : data) {
std::cout << i++ << ": '" << entry.key << "'\n";
}
}
std::cout << "Sorting...";
std::sort(std::begin(data), std::end(data), less);
std::cout << " Done.\n";
{ std::cout << "Sorted data:\n";
int i = 0;
for (const GridLabel &entry : data) {
std::cout << i++ << ": '" << entry.key << "'\n";
}
}
}
输出:
Original data:
0: 'K31,173,8.37,1'
1: 'K29,143,3.36,2'
2: 'K29,107,4.56,3'
3: 'K30,133,5.97,4'
4: 'K30,153,2.38,5'
5: 'J27,203,1.86,6'
6: 'J27,143,1.59,7'
7: 'I26,73,7.66,8'
8: 'I27,134,2.86,9'
Sorting... Done.
Sorted data:
0: 'I26,73,7.66,8'
1: 'I27,134,2.86,9'
2: 'J27,203,1.86,6'
3: 'J27,143,1.59,7'
4: 'K29,143,3.36,2'
5: 'K29,107,4.56,3'
6: 'K30,133,5.97,4'
7: 'K30,153,2.38,5'
8: 'K31,173,8.37,1'
Live Demo on coliru
请注意(根据谓词
less()的实现方式)，有很多元素被认为是相等的:I26,73,7.66,8与I27,134,2.86,9 J27,203,1.86,6与J27,143,1.59,7 这些元素将在排序后以任意顺序出现。
或者，可以使用
std::stable_sort() 在这种情况下将保留原始顺序。关于c++ - std::sort函数出现问题。经过2轮迭代，似乎对1个元素总是具有null值，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/58761130/