Training and consultancy for testing laboratories.

Archive for the ‘R Language’ Category

Using R to generate a random sampling table

Sampling 8

The open source R programing language is a free software environment for statistical computing and graphics, and is easy to master. The official website is https://www.r-project.org/ . It can run on a wide variety of UNIX platforms, Windows and MacOS.

On September 24, 2016, this blog site published an article on how to use R to generate random numbers (https://consultglp.com/2016/09/24/how-to-use-r-to-generate-random-numbers/) .   In light of the newly revised ISO/IEC 17025 accreditation standards embracing sampling as another important criterion for technical competence assessment, the random number function of R becomes very handy for cargo surveyors and samplers to prepare their sampling plan on cargo shipment.

We can use the random number function of R to create a random number table to suit the needs in randomly selecting samples for laboratory quality analysis.

For example, there is a shipment of 1000 bags of coffee beans in a warehouse to be surveyed prior to be dispatched to port. The buyer requires a 5% sampling for laboratory quality testing.  That means some 50 bags have to be random selected before composite a portion of each bag into a suitable sized test sample through a quartering sub-sampling process.

The sampling plan, therefore, can be the following process:

1.  Label each bag with a sequential number

2.  Create 50 numbers in a random number table with the R command language:

> RandSampling=sample(500,50)

> dim(RandSampling)=c(10,5)

> RandSampling

[,1]   [,2]   [,3]   [,4]   [,5]

[1,]  154  424   84  486   82

[2,]   78  214  275  498  388

[3,]   93  104  478  148  258

[4,]  229  283   96  479  489

[5,]  487  211  216   59  263

[6,]   94  450   47  201  105

[7,]  330  121  130  276   56

[8,]   11  415  303  240  407

[9,]  427   60   71  142  409

[10,]  101  238  228  441  355

>

3.  Sample a portion (say, 500g) of the coffee beans from the bags with these selected numbers into a large sampling bag.

4.  Conduct a sample quartering process on site to reduce the test sample size to about 2.5 kg before sending to the laboratory for analysis.

 

 

 

How to ensure your random sampling process is really random?

Cargo                                       How to ensure your simple random sampling is really random

R techniques in generating random numbers

r-techniques-in-generating-random-numbers

Using R to perform simple linear regression

using-r-to-perform-simple-linear-regression

Having a taste of R language

having-a-taste-of-r-language

Interesting graph plotting with R

interesting-graph-plotting-with-r

Using R to simulate the Central Limit Theorem

using-r-to-simulate-the-central-limit-theorem