Question

当尝试使用带有两个数字和容差参数的testthat::expect_equal()时，它会在参数按特定顺序传递时传递，但如果两个数字交换参数位置则失败。我注意到这个函数使用基础包中的all.equal()引用，并且该函数在交换参数时也有通过/失败的区别。

无论两个函数的前两个参数的顺序如何，我都期望得到相同的答案。如果这不是正确的期望，请告诉我。

library(testthat)

# expect_equal does not throw error with one pair of numbers to compare
expect_equal(5, 1, tolerance=1)

# But does when the two numbers are reversed in their arguments
tryCatch(expect_equal(1, 5, tolerance=1), expectation_failure=conditionMessage)
#> [1] "1 not equal to 5.\n1/1 mismatches\n[1] 1 - 5 == -4\n"

# Since this seems to reference `all.equal()` I tried there too, and see an issue:
all.equal(1, 5, tolerance=1)
#> [1] "Mean absolute difference: 4"
all.equal(5, 1, tolerance=1)
#> [1] TRUE

# My session info:
sessionInfo()
#> R version 3.3.3 (2017-03-06)
#> Platform: x86_64-w64-mingw32/x64 (64-bit)
#> Running under: Windows 7 x64 (build 7601) Service Pack 1
#> 
#> locale:
#> [1] LC_COLLATE=English_United States.1252 
#> [2] LC_CTYPE=English_United States.1252   
#> [3] LC_MONETARY=English_United States.1252
#> [4] LC_NUMERIC=C                          
#> [5] LC_TIME=English_United States.1252    
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] testthat_1.0.2
#> 
#> loaded via a namespace (and not attached):
#>  [1] backports_1.0.5 R6_2.2.1        magrittr_1.5    rprojroot_1.2  
#>  [5] tools_3.3.3     htmltools_0.3.6 yaml_2.1.14     crayon_1.3.2   
#>  [9] Rcpp_0.12.10    stringi_1.1.5   rmarkdown_1.5   knitr_1.15.1   
#> [13] stringr_1.2.0   digest_0.6.12   evaluate_0.10

Answer 1

TL;博士

您的容忍度大于

mean(abs(target-current)) / abs(target)
mean(5 - 1) / 5
4 / 5
0.8

因此，在比较0.8 < 1之后函数会返回，因为您已允许它通过此容差检查

完整答案

all.equal()函数的参数为target和current

如果您深入研究代码，当target为5且current为1时，它会计算平均绝对差值

mean(abs(target - current))
# 4

然后在目标和公差之间进行比较，在这种情况下是

5 > 1
## TRUE

由于这是真的，它然后计算相对差

4 / 5 
## 0.8

这里，0.8不大于容差，因此它返回TRUE的函数，即

all.equal(5, 1, tolerance = 1)
# [1] TRUE

因此，tolerance的值用于比较相对差异。这就是容差默认为1.5e-8

的小值的原因

我已经从all.equal.numeric获取相关代码，仅删除了感兴趣的内容，以便您可以更清楚地看到它

allEqual <- function (target, current, tolerance = sqrt(.Machine$double.eps)) 
{
    msg <- NULL
    target <- as.vector(target)
    current <- as.vector(current)
    out <- is.na(target)

    out <- out | target == current

    if (all(out)) 
        return(if (is.null(msg)) TRUE else msg)

    target <- target[!out]
    current <- current[!out]

    xy <- mean(abs(target - current))

    ## THIS BIT HERE vv
    what <- {
        xn <- mean(abs(target))
        # print(paste0("xn: ", xn))
        if (is.finite(xn) && xn > tolerance) {
            #print("xn (target) is GREATER than the tolerance")
            xy <- xy/xn
            #print(paste0("relative difference: ", xy))
            "relative"
        }
        else{
            # print("xn (target) is SMALLER than the tolerance")
            "absolute"
        } 
    }
    ## THIS BIT HERE ^^

    if (is.na(xy) || xy > tolerance) 
        #print("xy is GREATER than the tolerance")
        msg <- c(msg, paste("Mean", what, "difference:", format(xy)))
    if (is.null(msg)) 
        TRUE
    else msg
}

allEqual(5, 1, tolerance = 0.79)
# [1] "Mean relative difference: 0.8"
allEqual(5, 1, tolerance = 0.81)
# [1] TRUE
allEqual(5, 1, tolerance = 1)
# [1] TRUE
allEqual(1, 5, tolerance = 1)
# [1] "Mean absolute difference: 4"

expect_equal（）以一个顺序传递参数，如果参数被交换则失败

1 个答案:

TL;博士

完整答案