I have the following data.frame ::
df <- data.frame(Qtd=c(100,200,300,400,500),
op=c('V','C','C','V','V'), stringsAsFactors=F)
How can I turn the values in the Qtd column to negative if the value of the column op is V ??
I tried this command but it failed:
Teste <- within(df, Qtd[op == 'V'] <- -Qtd[])
Warning message:
In Qtd[op == "V"] <- -Qtd[] :
number of items to replace is not a multiple of replacement length
Your code would also work normally, what you were missing was to put the same logical condition inside -Qtd[] . Correcting:
within(df, Qtd[op == 'V'] <- -Qtd[op == 'V'])
Qtd op
1 -100 V
2 200 C
3 300 C
4 -400 V
5 -500 V
ifelse can help you here:
df <- data.frame(Qtd=c(100,200,300,400,500),
op=c('V','C','C','V','V'), stringsAsFactors=F)
df$Qtd <- ifelse(df$op == "V", -df$Qtd, df$Qtd)
Or you can also use which to first filter the rows, and then apply the operation:
df <- data.frame(Qtd=c(100,200,300,400,500),
op=c('V','C','C','V','V'), stringsAsFactors=F)
rows <- which(df$op == "V")
df$Qtd[rows] = -df$Qtd[rows]