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| gendf <- function() { | |
| a <- data.frame(x = rnorm(200, 1, 1), y = rnorm(200, 3, 1)) | |
| b <- data.frame(x = rnorm(200, 9, 1), y = rnorm(200, 10, 1)) | |
| z <- c(rep(1, 200), rep(2, 200)) | |
| cbind(rbind(a, b), z)[sample(1:400),] | |
| } | |
| df1 <- gendf() | |
| df2 <- gendf() | |
| df3 <- gendf() | |
| ## Suppose you have three data.frames, df1, df2, df3 | |
| ## task: remove rows with z == 1 and calculate the mean of x * y | |
| df1no1 <- df1[df1$z!=1,] | |
| mean(df1no1$x * df1no1$y) | |
| ## Copy and paste? | |
| df2no1 <- df2[df2$z!=1,] | |
| mean(df2no1$x * df2no1$y) | |
| ## and again? | |
| df3no1 <- df3[df3$z!=1,] | |
| mean(df3no1$x * df3no1$y) | |
| ## Don't repeat yourself | |
| removez1mean <- function(df) { | |
| dfno1 <- df[df$z != 1,] | |
| mean(dfno1$x * dfno1$y) | |
| } | |
| removez1mean(df1) | |
| removez1mean(df2) | |
| removez1mean(df3) | |
| ## actual this itself is repeat also. Further remove the repetition | |
| sapply(list(df1, df2, df3), removez1mean) |
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