How can i do tapply with filter on one of the variables

Question

I'm using the tapply function in order to get the count of variable over another variable. Here is the line of code: tapply(vip$VAR1,vip$VAR2,length)

However, I would like to filter only observations that have the value "1" on vip$VAR1, can I do this with tapply?

dat <- read.table(text = " VAR1 VAR2 admit       num
 0        0        0         7
 0        0        1         1
 0        1        0         3
 0        1        1         7
 1        0        0         5
 1        0        1         1
 1        1        0         0
 1        1        1         6", header = TRUE)

Where is "VAR1" and "VAR2" in your sample data? – A5C1D2H2I1M1N2O1R2T1 Apr 14 '14 at 05:50 — A5C1D2H2I1M1N2O1R2T1, Apr 14 '14 at 05:50
fixed the dataframe, thanks – mql4beginner Apr 14 '14 at 06:16 — mql4beginner, Apr 14 '14 at 06:16

Joe · Accepted Answer · 2014-04-14T06:38:18.760

2

Would this do the trick?

tapply(dat[dat$VAR1==1,]$VAR1,dat[dat$VAR1==1,]$VAR2,length)

Or the simpler (from Ananda Mahto's comment):

with(dat[dat$VAR1 == 1, ], tapply(VAR1, VAR2, length))

edited Apr 14 '14 at 06:38

answered Apr 14 '14 at 06:06

Joe

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3

I find the following a little easier to read: `with(dat[dat$VAR1 == 1, ], tapply(VAR1, VAR2, length))`. – A5C1D2H2I1M1N2O1R2T1 Apr 14 '14 at 06:36

How can i do tapply with filter on one of the variables

1 Answers1