r - how to retrieve all the records from dataframe with a particular column having two values -


i have data frame called "specdata"

this dataframe specdata consists:

head(specdata)           date sulfate nitrate id 1: 2003-01-01             na          na     1 2: 2003-01-02             na          na     1 3: 2003-01-03             na          na     1 4: 2003-01-04             na          na     1 5: 2003-01-05             na          na     1 6: 2003-01-06             na          na     1  tail(specdata)           date sulfate nitrate  id 1: 2004-12-26      na      na 332 2: 2004-12-27      na      na 332 3: 2004-12-28      na      na 332 4: 2004-12-29      na      na 332 5: 2004-12-30      na      na 332 6: 2004-12-31      na      na 332 

the data frame contains id column 1 332 , sulfate has values other na's.

when tried retrieve values of sulfate column id column==1, worked used below code that:

subset(specdata$sulfate,specdata$id==1)  

what need should able retrieve values of sulfate column id = 1:20, didn't worked.

i used below code that:

subset(specdata$sulfate,specdata$id==1)   warning message: in specdata$id == 1:20 :   longer object length not multiple of shorter object length 

can 1 me on this?

if subsetting single vector,

 specdata$sulfate[specdata$id %in% 1:20] 

should work fine. subset more useful subsetting entire data.frame like

 subset(specdata, id %in% 1:20) 

and allows skip explicit indexing ("$" or "[,]") though not work when try use variables column names.


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