[R] Count of unique factors within another factor

[Birdnerd]

I have a data frame with two factors (sampling 'unit', 'species'). I want to
calculate the number of unique 'species' per 'unit.' I can calculate the
number of unique values for each variable separately, but can't get a count
for each ‘unit’.

> data=read.csv("C:/Desktop/sr_sort_practice.csv")
> attach(data)

> data[1:10,]
   unit species
1   123    ACMA
2   123    LIDE
3   123    LIDE
4   123    SESE
5   123    SESE
6   123    SESE
7   345    HEAR
8   345    LOHI
9   345    QUAG
10  345    TODI…..

> sr.unique<- lapply (data, unique)
$unit
[1] 123 345 216
$species
 [1] ACMA  LIDE  SESE  HEAR  LOHI  QUAG  TODI  UMCA  ARSP  LIDE

> sapply (sr.unique,length)
    unit species 
      3      10

Then, I get stuck here because this unique species count is not given for
each ‘unit’.
What I'd like to get is:

unit species
123    3
345    4
216    --

Thanks--

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