spore234 - 8 months ago 31

R Question

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
```

Source (Stackoverflow)