create binary matrix from data.frame

Question

How can I create a binary matrix from a data.frame with two columns where the first column represents e.g. species and the other their region? The data.frame is in tall format as seen below

species region
species1 1
species1 2
species1 3
species2 2
species2 4
species2 5
species2 6
species3 1
species3 2
species4 5
species5 3
species5 4

And the matrix would have all unique species as rows and all unique regions as columns. The matrix would be filled with 1s for species present and 0s for species absent, as below

         1  2  3  4  5  6
species1 1  1  1  0  0  0
species2 0  1  0  1  1  1
species3 1  1  0  0  0  0
species4 0  0  0  0  1  0
species5 0  0  1  1  0  0

Any pointers would be very much appreciated, thanks!

Pop · Accepted Answer · 2014-03-06 10:12:20Z

6

You are looking for the function table whose documentation is here

If your data.frame is df, you just have to do

table(df)

answered Mar 6, 2014 at 10:12

Pop

12.5k5 gold badges57 silver badges70 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

jO. Over a year ago

Thanks for commenting. Dooh' embarrassingly easy.

perepm Over a year ago

I'm getting an error: attempt to make a table with >= 2^31 elements. Is there a way to do it with bigger dataframes?

droopy · Accepted Answer · 2014-03-06 10:12:47Z

3

an other possibility :

xtabs(~species+region, data=tab)

answered Mar 6, 2014 at 10:12

droopy

2,8281 gold badge16 silver badges12 bronze badges

2 Comments

jO. Over a year ago

Thanks for commenting and for an alternative solution.

droopy Over a year ago

xtabs fonction as table is dedicated to create contingency tables, you just have to indicate which lines and columns you want to cross

Collectives™ on Stack Overflow

create binary matrix from data.frame

2 Answers 2

2 Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Linked

Related