我在数据框中有一些医院数据,从csv读入.我尝试按用户定义的列排序数据框col,然后按医院的名称排序,如下所示:
col <- 'Hospital.30.Day.Death..Mortality..Rates.from.Pneumonia'
hospitals.sorted <- hospitals[order(hospitals[,col], hospitals$Hospital.Name),]
但我想我错过了一些东西; 它看起来col像字符串:
> hospitals.sorted
... # so far so good # ...
2749 10.0
2831 10.0
2891 10.0
2837 10.1
2824 10.1
2774 10.1
... # not so good # ...
2856 15.7
2834 15.9
2797 16.0
2835 7.4
2850 7.7
2789 8.1
... # there are some non-numeric values at the very bottom # ...
2806 9.9
2867 9.9
2884 9.9
2808 Not Available
2913 Not Available …我正在深入研究OpenCV的SIFT描述符提取实现.我发现了一些令人费解的代码来获得兴趣点邻域的半径.下面是带注释的代码,变量名称更改为更具描述性:
// keep octave below 256 (255 is 1111 1111)
int octave = kpt.octave & 255;
// if octave is >= 128, ...????
octave = octave < 128 ? octave : (-128 | octave);
// 1/2^absval(octave)
float scale = octave >= 0 ? 1.0f/(1 << octave) : (float)(1 << -octave);
// multiply the point's radius by the calculated scale
float scl = kpt.size * 0.5f * scale;
// the constant sclFactor is 3 and has the following comment: …