R boxplot with which function

I have data from 2 field sampling campaigns. I have organised the data severeal columns and rows:

• Data = sample points
• Columns = elements (1,...,n) , season, Sampletype and some others.

Add. info on Columns:

• season = 1,2 (discriminating between seasons)
• sampletype = 1,2,3 (discriminating between sampletypes)

These 2 columns are in factor format.

What I want: A boxplot which shows the boxplot for an element i for the season 1 and for season 2 (In one graph). However, not over all sampletypes but only 1, e.g:

boxplot(element i ~ Season)  

This would give 开发者_如何转开发me the boxplot of the data of element i over all sample types but differentiated between the seasons. But I just want it for 1 sampletype.

How do I do this?

Use the subset parameter:

boxplot(element~Season,data=Data,subset=sampletype==1)