CODEWITHSUNDEEP
rdata.tabledplyrcalculation
jypst2003
jypst2003

Reputation: 131

How to calculate a value basing on several variables?

I have a dataset (df) like this:

Iso conc.   rep time    OD
1   1      1    0     0.2
1   1.5    2    0     0.2
1   2      3    0     0.2
2   1      1    0     0.3
2   1.5    2    0     0.25
2   2      3    0     0.3
1   1      1    1     0.4
1   1.5    2    1     0.35
1   2      3    1     0.38
2   1      1    1     0.4
2   1.5    2    1     0.45
2   2      3    1     0.43

And I want to get the result growth=OD(time=1)-OD(time=0) basing on Iso, conc, and rep.

The output would be like this:

Iso conc.   rep time    growth
1   1      1    1      0.2
1   1.5    2    1      0.15
1   2      3    1      0.18
2   1      1    1      0.1
2   1.5    2    1      0.2
2   2      3    1      0.13

I have been thinking to use data.table to calculate the growth. 

DT <- as.data.table(df)
DT[, , by = .(Iso,conc.,rep,set)]

But I don't know how to write the part before two comma. Could somebody help me?

Upvotes: 1

Views: 53

Answers (2)

David Robinson
David Robinson

Reputation: 78590

You can do this with:

DT [, list(growth = OD[time == 1] - OD[time == 0]), by=.(Iso,conc.,rep)]

Or alternatively, if you are sure there are only two values in each group:

DT [order(time), list(growth = diff(OD), by=.(Iso,conc.,rep)]

Upvotes: 1

mtoto
mtoto

Reputation: 24178

Using data.table you can simply do:

dt[,.(growth = OD[time==1]-OD[time==0]),.(Iso,conc.,rep)]
#   Iso conc. rep growth
#1:   1   1.0   1   0.20
#2:   1   1.5   2   0.15
#3:   1   2.0   3   0.18
#4:   2   1.0   1   0.10
#5:   2   1.5   2   0.20
#6:   2   2.0   3   0.13

Upvotes: 1

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