如何从频率表中绘制密度 [英] How to Plot Density from Frequency Table

问题描述

给出下面的频率表:

> print(dat)
V1    V2
1  1 11613
2  2  6517
3  3  2442
4  4   687
5  5   159
6  6    29

# V1 = Score
# V2 = Frequency

我们如何绘制密度，(即 y 轴范围从 0 到 1.0).

How can we plot the density, (i.e. y-axis range from 0 to 1.0).

目前我有以下频率图:

plot(0,main="table",type="n");
lines(dat,lty=1)

# I need to use lines() and plot() here, 
# because need to make multiple lines in single plot

不确定如何处理密度.

推荐答案

假设每一行都是一个单独的块，那么每个块的密度将为 V2/sum(V2).

The density of each block would be V2 / sum(V2) assuming that each row is a separate block.

为了您的数据

dat <- data.frame(V1 = 1:6, V2 = c(11613, 6517, 2442, 687, 159, 29))

我明白了:

> with(dat, V2 / sum(V2))
[1] 0.541474332 0.303865342 0.113862079 0.032032452 0.007413624 0.001352170

我们可以使用 R 的工具进行检查.首先展开你的紧凑频率表

Which we can check using R's tools. First expand your compact frequency table

dat2 <- unlist(apply(dat, 1, function(x) rep(x[1], x[2])))

然后使用hist()来计算我们想要的值

Then use hist() to compute the values we want

dens <- hist(dat2, breaks = c(0:6), plot = FALSE)

查看生成的对象:

> str(dens)
List of 7
 $ breaks     : int [1:7] 0 1 2 3 4 5 6
 $ counts     : int [1:6] 11613 6517 2442 687 159 29
 $ intensities: num [1:6] 0.54147 0.30387 0.11386 0.03203 0.00741 ...
 $ density    : num [1:6] 0.54147 0.30387 0.11386 0.03203 0.00741 ...
     $ mids       : num [1:6] 0.5 1.5 2.5 3.5 4.5 5.5
 $ xname      : chr "dat2"
 $ equidist   : logi TRUE
 - attr(*, "class")= chr "histogram"

注意 密度 组件是:

> dens$density
[1] 0.541474332 0.303865342 0.113862079 0.032032452 0.007413624 0.001352170

这与我从原始频率表表示中手工计算的结果一致.

Which concurs with my by-hand calculation from the original frequency table representation.

至于绘图，如果您只想绘制密度，请尝试:

As for the plotting, if you just want to draw densities instead then try:

dat <- transform(dat, density = V2 / sum(V2))
plot(density ~ V1, data = dat, type = "n")
lines(density ~ V1, data = dat, col = "red")

如果你想强制轴限制做:

If you want to force axis limits do:

plot(density ~ V1, data = dat, type = "n", ylim = c(0,1))
lines(density ~ V1, data = dat, col = "red")

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