spore234 spore234 - 1 month ago 5
R Question

calling custom function with indexed vector argument

I have this custom function:

f <- function(N, zero_per, sed) {
set.seed(sed)
M <- N-(N*zero_per)
y_g <- rgamma(M, shape=rnorm(M,1,2), rate=rnorm(M,1,2))
df_g <- data.frame(y=y_g)
df_l <- data.frame(y=rep(0, N-M))
df <- rbind(df_g, df_l)
return(df)
}


this function is part of a loop where I use a sequence for the second argument:

> sq <- seq(0.05, 0.7, 0.05)
> sq
[1] 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70


the 12th position has value 0.6:

> sq[12]
[1] 0.6


However, when I call the function, once with the numeric argument 0.6, and once with sq[12], I get different results:

> head(f(5000, sq[12], 1))
y
1 NaN
2 NaN
3 NaN
4 0.7547084
5 1.0643216
6 NaN
Warning message:
In rgamma(M, shape = rnorm(M, 1, 2), rate = rnorm(M, 1, 2)) : NAs produced

> head(f(5000, 0.6, 1))
y
1 NaN
2 NaN
3 NaN
4 0.8990203
5 1.0719659
6 NaN
Warning message:
In rgamma(M, shape = rnorm(M, 1, 2), rate = rnorm(M, 1, 2)) : NAs produced


I use the same seed.

Strangely, this does not happen when I use 0.5:

> head(f(5000, sq[10], 1))
y
1 NaN
2 NaN
3 NaN
4 0.4426849
5 NaN
6 NaN
Warning message:
In rgamma(M, shape = rnorm(M, 1, 2), rate = rnorm(M, 1, 2)) : NAs produced
> head(f(5000, 0.5, 1))
y
1 NaN
2 NaN
3 NaN
4 0.4426849
5 NaN
6 NaN
Warning message:
In rgamma(M, shape = rnorm(M, 1, 2), rate = rnorm(M, 1, 2)) : NAs produced


The warnings can be ignored, they just happen because I stripped down my real function.

What is going on here?

Answer

The problem is that:

sq[12]==0.6
#[1] FALSE 

While

sq[10]==0.5
#[1] TRUE 

To see that, do the following:

options(digits = 20)

sq[12]
#[1] 0.60000000000000009

sq[10]
#[1] 0.5
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