[英]Why does as.integer64(“”) return 0 instead of NA_integer64_?
鑒於空字符串的基本as.integer()
強制是NA
而沒有警告,如:
str( as.integer(c('1234','5678','')) ) # int [1:3] 1234 5678 NA -- no warning
我很難理解為什么bit64::as.integer64()
在沒有警告的情況下bit64::as.integer64()
為零:
library('bit64')
str( as.integer64(c('1234','5678','')) ) # integer64 [1:3] 1234 5678 0 -- no warning
更奇怪的是比較:
str( as.integer(c('1234','5678','', 'Help me Stack Overflow')) )
# int [1:4] 1234 5678 NA NA -- coercion warning
有:
str( as.integer64(c('1234','5678','', 'Help me Stack Overflow')) )
# integer64 [1:4] 1234 5678 0 NA -- no warning
我的解決方法失敗了:
asInt64 <- function(s){
require(bit64)
ifelse(grepl('^\\d+$',s), as.integer64(s), NA_integer64_)
}
str(asInt64(c('1234','5678','', 'Help me Stack Overflow')) )
# num [1:4] 6.10e-321 2.81e-320 0.00 0.00
# huh?
所以,我問:
為什么會這樣?
什么是最好的解決方法?
正如@ lukeA的評論指出的那樣, as.integer64.character
的來源是:
SEXP as_integer64_character(SEXP x_, SEXP ret_){
long long i, n = LENGTH(ret_);
long long * ret = (long long *) REAL(ret_);
const char * str;
char * endpointer;
for(i=0; i<n; i++){
str = CHAR(STRING_ELT(x_, i)); endpointer = (char *)str; // thanks to Murray Stokely 28.1.2012
ret[i] = strtoll(str, &endpointer, 10);
if (*endpointer)
ret[i] = NA_INTEGER64;
}
return ret_;
}
當調用無效值(例如""
或"ABCD"
strtoll("")
, strtoll("")
返回零並顯示錯誤。 一個參考strtoll
示例處理如下:
/* If the result is 0, test for an error */
if (result == 0)
{
/* If a conversion error occurred, display a message and exit */
if (errno == EINVAL)
{
printf("Conversion error occurred: %d\n", errno);
exit(0);
}
/* If the value provided was out of range, display a warning message */
if (errno == ERANGE)
printf("The value provided was out of range\n");
}
所以我現在要弄清楚的是為什么*endpointer
正在評估為FALSE。 (敬請關注...)
以下是模仿base as.integer
行為的解決方法:
library(bit64)
charToInt64 <- function(s){
stopifnot( is.character(s) )
x <- as.integer64(s)
# as.integer64("") unexpectedly returns zero without warning.
# Overwrite this result to return NA without warning, similar to base as.integer("")
x[s==""] <- NA_integer64_
# as.integer64("ABC") unexpectedly returns zero without warning.
# Overwrite this result to return NA with same coercion warning as base as.integer("ABC")
bad_strings <- grepl('\\D',s) # thanks to @lukeA for the hint
if( any(bad_strings) ){
warning('NAs introduced by coercion')
x[bad_strings] <- NA_integer64_
}
x
}
要看到這個有效:
test_string <- c('1234','5678','', 'Help me Stack Overflow')
charToInt64(test_string) # returns int64 [1] 1234 5678 <NA> <NA> with warning
charToInt64(head(test_string,-1)) # returns int64 [1] 1234 5678 <NA> without warning
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