weibull 是该数据的正确分布吗？如何使用 R 找到最佳参数？答案

【问题标题】：Is weibull the right distribution for this data? How do i find the best parameters using R?weibull 是该数据的正确分布吗？如何使用 R 找到最佳参数？
【发布时间】：2022-01-08 23:38:47
【问题描述】：

我有多个 (1000s) 事件组的一些时间发生数据。我需要对显示相似分布的事件组进行聚类，并找到每个聚类的参数。每个事件组有 5-15 个数据点。我从 50 个事件组中随机抽取样本，并将它们绘制成频率与时间的关系图。

对我来说，分布似乎是 Weibull，现在我正在寻找参数，但我一直无法找到稳定的参数。我已经使用 nls 包来查找事件组的稳定参数。

dat <- data.frame(x=single_event$time, y=single_event$freq_density)
pars <- expand.grid(a=seq(0.01, 10, len=20),
                b=seq(1, 50, len=20))
res <- nls2(y ~ ((a/b) * ((x/b)^(a-1)) * exp(- (x/b)^a)), data=dat,
        start=pars, algorithm='brute-force')
res1 <- nls(y ~ ((a/b) * ((x/b)^(a-1)) * exp(- (x/b)^a)), data=dat,
        start=as.list(coef(res)))

但我无法获得有意义的输出。对于大多数事件组，我收到错误 Error in nls(y ~ ((a/b) * ((x/b)^(a - 1)) * exp(-(x/b)^a)), data = dat, : singular gradient

现在，我想知道我是否选择了正确的发行版。

我如何为此获得正确的分布？以及如何找到参数？

这是一些示例数据：

event_group <- c('group_A', 'group_B', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_A', 'group_C', 'group_B', 'group_D', 'group_E', 'group_B', 'group_D', 'group_E', 'group_B', 'group_E', 'group_B', 'group_D', 'group_E', 'group_E')

freq_density <- c(0.005747126, 0.015151515, 0.057471264, 0.089552239, 0.015151515, 0.104477612, 0.033057851, 0.103448276, 0.28358209, 0.106060606, 0.044776119, 0.140495868, 0.25862069, 0.298507463, 0.181818182, 0.164179104, 0.090909091, 0.206896552, 0.164179104, 0.212121212, 0.268656716, 0.347107438, 0.247126437, 0.059701493, 0.151515152, 0.179104478, 0.190082645, 0.114942529, 0.074626866, 0.121212121, 0.074626866, 0.05785124, 0.005747126, 0.029850746, 0.075757576, 0.119402985, 0.033057851, 0.045454545, 0.029850746, 0.033057851, 0.060606061, 0.049586777, 0.015151515, 0.014925373, 0.008264463, 0.016528926)

time_min <- c(10, 30, 40, 45, 45, 45, 55, 55, 60, 60, 60, 70, 70, 75, 75, 75, 85, 85, 90, 90, 90, 100, 100, 105, 105, 105, 115, 115, 120, 120, 120, 130, 130, 135, 135, 135, 145, 150, 150, 160, 165, 175, 180, 195, 235, 250)

sample_data <- data.frame(event_group, time_min, freq_density, stringsAsFactors=FALSE)

【问题讨论】：

标签： r distribution weibull gamma-distribution

【解决方案1】：

fitdistrplus::fitdist()可用于判断参数：

fitdistrplus::fitdist(sample_data$freq_density, distr = "gamma")
#> Fitting of the distribution ' gamma ' by maximum likelihood 
#> Parameters:
#>       estimate Std. Error
#> shape  1.25139  0.2341895
#> rate  11.51292  2.6352952

fitdistrplus::fitdist(sample_data$freq_density, distr = "weibull")
#> Fitting of the distribution ' weibull ' by maximum likelihood 
#> Parameters:
#>        estimate Std. Error
#> shape 1.1657556 0.13768844
#> scale 0.1145993 0.01526602

# Use a Cullen and Frey graph to choose the 'best' fitting distribution
fitdistrplus::descdist(sample_data$freq_density)

#> summary statistics
#> ------
#> min:  0.005747126   max:  0.3471074 
#> median:  0.08265491 
#> mean:  0.1086957 
#> estimated sd:  0.09034791 
#> estimated skewness:  0.9060949 
#> estimated kurtosis:  2.942441

^{由reprex package (v2.0.1) 于 2021-12-02 创建}

根据 Cullen 和 Frey 图，对于给定数据，伽马分布似乎是一个不错的选择。

如果您想将fitdistrplus::fitdist() 应用于多个组，例如可以使用purrr::map()：

    library(dplyr)   
    sample_data %>%
      split(.$event_group) %>%
      purrr::map(~fitdistrplus::fitdist(.$freq_density, distr = "gamma"))
    #> $group_A
    #> Fitting of the distribution ' gamma ' by maximum likelihood 
    #> Parameters:
    #>        estimate Std. Error
    #> shape 0.8847797  0.3852533
    #> rate  7.0784485  4.0716225
    #> 
    #> $group_B
    #> Fitting of the distribution ' gamma ' by maximum likelihood 
    #> Parameters:
    #>        estimate Std. Error
    #> shape  1.465481  0.5678731
    #> rate  16.121401  7.4261676
    #> 
    #> $group_C
    #> Fitting of the distribution ' gamma ' by maximum likelihood 
    #> Parameters:
    #>        estimate Std. Error
    #> shape  1.906359  0.9434099
    #> rate  13.344416  7.5468387
    #> 
    #> $group_D
    #> Fitting of the distribution ' gamma ' by maximum likelihood 
    #> Parameters:
    #>       estimate Std. Error
    #> shape  1.71704  0.7441117
    #> rate  15.45395  7.7658146
    #> 
    #> $group_E
    #> Fitting of the distribution ' gamma ' by maximum likelihood 
    #> Parameters:
    #>        estimate Std. Error
    #> shape  1.104798  0.4184115
    #> rate  12.152399  5.7735560

【讨论】：