How to split data into training/testing sets using sample function

r sample
Susie Humby picture Susie Humby · Jun 19, 2013 · Viewed 495.2k times · Source

I've just started using R and I'm not sure how to incorporate my dataset with the following sample code: 

sample(x, size, replace = FALSE, prob = NULL)

I have a dataset that I need to put into a training (75%) and testing (25%) set. I'm not sure what information I'm supposed to put into the x and size? Is x the dataset file, and size how many samples I have?

Answer

dickoa picture dickoa · Jun 19, 2013

There are numerous approaches to achieve data partitioning. For a more complete approach take a look at the createDataPartition function in the caTools package.

Here is a simple example:

data(mtcars)

## 75% of the sample size
smp_size <- floor(0.75 * nrow(mtcars))

## set the seed to make your partition reproducible
set.seed(123)
train_ind <- sample(seq_len(nrow(mtcars)), size = smp_size)

train <- mtcars[train_ind, ]
test <- mtcars[-train_ind, ]

Related questions

Random sample of rows from subset of an R dataframe

Is there a good way of getting a sample of rows from part of a dataframe? If I just have data such as gender <- c("F", "M", "M", "F", "F", "M", "F", "F") age <- c(23, 25, 27, 29, 31, 33, 35, 37) then …

Read More
Sample n random rows per group in a dataframe

From these questions - Random sample of rows from subset of an R dataframe & Sample random rows in dataframe I can easily see how to randomly sample (select) 'n' rows from a df, or 'n' rows that originate from …

Read More
Take randomly sample based on groups

I have a data frame made by almost 50,000 rows spread in 15 different IDs (every ID has thousands of observations). Data frame looks like: ID Year Temp ph 1 P1 1996 11.3 6.80 2 P1 1996 9.7 6.90 3 P1 1997 9.8 7.10 ... 2000 P2 1997 10.5 6.90 2001 P2 1997 9.9 7.00 2002 P2 1997 10.0 6.93 I want to take 500 random rows for …

Read More