meitei
December 14, 2020, 10:32pm
1
Hello everyone,
How can I get both ordinate and abscissa from the CDF plot?

For example, in the code below; I want to have ordinate for x-value=50.
Likewise, x-value when y-value=0.5.

Thanks

```
set.seed(1000)
a <- rnorm(10000, 1, 100)
aCDFcolor <- rgb(1,0,0)
plot(ecdf(a), col=aCDFcolor, main=NA)
```

DavoWW
December 15, 2020, 6:06am
2
Hi @meitei ,
Try this:

```
set.seed(1000)
a <- rnorm(10000, 1, 100)
aCDFcolor <- rgb(1,0,0)
plot(ecdf(a), col=aCDFcolor, main=NA)
summary(ecdf(a))
#> Empirical CDF: 10000 unique values with summary
#> Min. 1st Qu. Median Mean 3rd Qu. Max.
#> -355.179 -66.385 0.873 1.115 68.902 374.914
# Abscissa (x) from ordinate (y)
quantile(ecdf(a), c(0.2, 0.5, 0.8))
#> 20% 50% 80%
#> -83.123396 0.872981 85.676709
# Ordinate from abscissa (bit clunky; must be a better way?)
library(Hmisc)
#> Loading required package: lattice
#> Loading required package: survival
#> Loading required package: Formula
#> Loading required package: ggplot2
#>
#> Attaching package: 'Hmisc'
#> The following objects are masked from 'package:base':
#>
#> format.pval, units
```

```
Ecdf(a)
```

```
temp <- as.data.frame(Ecdf(a))
```

```
predict(loess(temp$y ~ temp$x), c(-100, 50, 180))
#> [1] 0.1605665 0.6833963 0.9724153
```

^{Created on 2020-12-15 by the reprex package (v0.3.0)}

1 Like

meitei
December 17, 2020, 1:12am
4
Could you further check why the quantiles are not estimated proportionately?
For example:

```
set.seed(10)
dat=runif(50,0,100)
cdf <- as.data.frame(Ecdf(dat))
colnames(cdf)=c("Temperature","probability")
temp=30
(percentile=predict(loess(cdf$probability ~ cdf$Temperature), temp))
set.seed(1000)
(u1 <- runif(1, 0, percentile))
(d1 <- quantile(ecdf(cdf$Temperature), u1))
d1=as.vector(d1)
percentile2=predict(loess(cdf$probability ~ cdf$Temperature),(temp-d1))
(u2=runif(1, 0, percentile2))
d2 <- ifelse(d1 <= temp,
quantile(ecdf(cdf$Temperature),u2),
0 )
d3 <- temp - (d1 + d2)
```

In the code above, I am expecting the temp=30 is disaggregated into 3 parts using the CDF.
The Sum of three parts should equal to temp.
However, I find d2>d1 in spite of having a lower percentile (i.e. percentile of d2<d1 so it should have a lower quantile).

Thanks

system
Closed
December 24, 2020, 1:12am
5
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