r语言 - 如何使用用户的按钮输入修改 RShiny 中的全局变量?

Question

我最近在下面的例子中挣扎了很多。在最基本的格式中，我有一个按钮some_button和一个输出result。当用户与平台交互时，我的意图是 运行曲线拟合方法(从包minpack.lm(并使用曲线拟合方法输出的四个参数来初始化Convert()函数。为了实现这一点，我的想法是初始化一个空的反应变量来存储系数(curvefit_coeff(和一个空的Convert()函数。然后，我使用observeEvent及其once参数集来TRUE确保它只运行一次。因此，这一次运行应该初始化我的curvefit_coeff以及我的Convert()函数 - 我想。但是，我无法从看起来observeEvent中"取出"这些值。我尝试使用winDialog以及我的result文本输出，但我总是以以下错误消息结束：

Error in .getReactiveEnvironment()$currentContext() : 
Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

library(shiny)
library(minpack.lm)
ui <- fluidPage(
actionButton("some_button", "Press me!"),
textOutput("result")
)

server <- function(input, output, session) {
# I tried to initialize my two variables in question as globals within the server function
curvefit_coeff <- reactive({ })
Convert <- function(x) { }
# This function fits a curve and returns the four parameters of the fitted curve
CurveFit <- function(pp) {
ds <- data.frame("x" = c(0.01, pp, 999, 1000), "y" = c(0, 0.5, 0.999, 1))
nlmInitial <- list(a = 0.5, power1 = -1, b = -1, power2 = 0.5)
m <- nlsLM(y ~ a*I(x^power1) + b*I(x^power2),
data = ds,
start = nlmInitial,
trace = F,
control = nls.lm.control(maxiter = 1024))
summary(m)$coefficients[,1]
}
# At the very first time the button is pressed, do the curve fit and using the parameters 
# from the curve fit, initialize the Convert() function that will be used later on
observeEvent(input$some_button, {
winDialog("ok", message = "Button pressed!")
curvefit_coeff <- reactive({ CurveFit(pp = 50) })
Convert  <- function(x) {
(curvefit_coeff()[1])*x^(curvefit_coeff()[2]) + (curvefit_coeff()[3])*x^(curvefit_coeff()[4])
} 
},ignoreInit = FALSE, once = TRUE)

# When I try to access either the coefficients from the curve fit or the Convert() 
# function itself, I get an error:
output$result <- curvefit_coeff()
output$result <- Convert(3)
}
shinyApp(ui, server)

Answer 1

好的，这里有一些事情发生。首先，如果要在输出中显示两个内容，则应具有两个不同的输出变量。接下来，错误消息来自您直接将向量分配给输出变量。当您想要显示通常在控制台中运行某些内容时看到的内容时，您应该将renderPrint与textOutput结合使用。如果您执行处理并且具有类似cat输出，则需要改用renderText。最后，您不希望使用赋值运算符 (<-( 从observeEvent中重新定义reactive值 - 您只想更新值(赋值运算符不会这样做(。我的建议是使用reactiveValues来跟踪这组操作和输出所需的一切，如下所示。

library(shiny)
library(minpack.lm)
ui <- fluidPage(
actionButton("some_button", "Press me!"),
textOutput("result1"),
textOutput("result2")
)

server <- function(input, output, session) {
# I tried to initialize my two variables in question as globals within the server function
curve_fit <- reactiveValues(coeffs = NA,
Convert = function(x) return(NA))
# This function fits a curve and returns the four parameters of the fitted curve
CurveFit <- function(pp) {
ds <- data.frame("x" = c(0.01, pp, 999, 1000), "y" = c(0, 0.5, 0.999, 1))
nlmInitial <- list(a = 0.5, power1 = -1, b = -1, power2 = 0.5)
m <- nlsLM(y ~ a*I(x^power1) + b*I(x^power2),
data = ds,
start = nlmInitial,
trace = F,
control = nls.lm.control(maxiter = 1024))
summary(m)$coefficients[,1]
}
# At the very first time the button is pressed, do the curve fit and using the parameters 
# from the curve fit, initialize the Convert() function that will be used later on
observeEvent(input$some_button, {
curve_fit[['coeffs']] <- CurveFit(pp = 50)
})
observeEvent(curve_fit[['coeffs']], {
curve_fit[['Convert']]  <- function(x) {
(curve_fit[['coeffs']][1])*x^(curve_fit[['coeffs']][2]) + (curve_fit[['coeffs']][3])*x^(curve_fit[['coeffs']][4])
}
})

# When I try to access either the coefficients from the curve fit or the Convert() 
# function itself, I get an error:
output$result1 <- renderPrint({
if(all(is.na(curve_fit[['coeffs']]))) return('Button not pressed.')
curve_fit[['coeffs']]
})
output$result2 <- renderPrint({
if(is.na(curve_fit$Convert(3))) return('Button not pressed.')
curve_fit$Convert(3)
})
}
shinyApp(ui, server)

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