sprintf 格式无效“%d" [英] sprintf invalid format '%d'

问题描述

这有效:

> sprintf('%d', c(1, 1.5))
[1] "1" "1"

这不会:

> sprintf('%d', c(1.5, 1))
Error in sprintf("%d", c(1.5, 1)) : 
  invalid format '%d'; use format %f, %e, %g or %a for numeric objects

为什么?

推荐答案

这实际上是一个非常有趣的问题.首先，%d 代表整数.如果可能，vector 参数会被回收，但如果它是 c(1.5, 1) 它将在 sprintf() 尝试替换 %d 时失败1.5(不是整数).

This is actually really interesting question. To start, %d stands for integer. The vector argument is recycled if possible but if it is c(1.5, 1) it will fail when sprintf() tries to replace %d with 1.5 (which is not integer).

我认为这可能与在 R 中 integer 和 double 都是数字模式的事实有关，例如:

I thought it might be related to the fact that in R both integer and double are numeric mode, for example:

storage.mode(c(1.5, 1))
# [1] "double"
storage.mode(c(1, 1.5))
# [1] "double"
mode(c(1,1.5))
# [1] "numeric"
mode(c(1.5,1))
# [1] "numeric"

因此两个向量都应该存储为双精度值.R 语言定义和 的文档?数字:

Thus both vectors should be stored as double. More info about vector in R language definition and in the documentation for ? numeric:

潜在的混淆是 R 使用模式数字"来表示双精度或整数""

The potential confusion is that R has used mode "numeric" to mean ‘double or integer’"

我可能在 底层 C 代码中找到了解释这是怎么回事:

I might have found the lines in the underlying C code which explain what is going on:

if(TYPEOF(_this) == REALSXP) {
double r = REAL(_this)[0];
if((double)((int) r) == r)
_this = coerceVector(_this, INTSXP);

此代码执行以下操作:如果向量类型为 REALSXP(表示数字)，则将向量的第一个成员转换为 double r.然后将 r 转换为整数，然后加倍，如果字节仍然相同，则将整个向量转换为 INTSXP.重要的是，这段代码只检查向量的第一个元素；如果该元素可以被强制为整数，则整个向量都被强制，否则代码会报错.

This code does the following: If the vector type is REALSXP (which means numeric) then convert first member of vector to double r. Then cast r as integer and then double and if bytes are still same convert whole vector as INTSXP. Importantly, this code only checks the first element of a vector; if that element can be coerced to integer, then the whole vector is coerced, otherwise the code gives an error.

为了测试这个假设，可以使用自定义的 sprintf() 编译 R，其中 double r = REAL(_this)[0]; 更改为 doubler = REAL(_this)[1]; 并测试 c(1.5, 1) 现在是否有效.

To test this hypothesis one could compile R with a custom sprintf() where double r = REAL(_this)[0]; is changed to double r = REAL(_this)[1]; and test whether c(1.5, 1) works now or not.

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