匹配来自两个数据框的列，并根据其他列的值进行过滤

Question

I have two dataframes with the same number of columns but different number of rows:

colA colB colC colD
xxx  303  200  A
yyy  111  20   B
zzz  24  188   C

I need to match colA from df1 to colA from df2 and select only the rows where df1$colB - df2$colC <= 2000

I tried to do the for loop but it didn't work:

for (i in nrow(df1)) {
    for (j in nrow(df2)) {
        df3 <- subset(merge(df2[j,], df1[i,], by="row.names", all=T), df2$colA[j] == df1$colA[i] && (df1$colB[i] - df2$colC[j]) <= abs(2000))
    }
}

What am I doing wrong? It doesn't give me any error but the new dataframe is empty.

Answer 1

If dplyr is an option, try this:

df1 %>%
    inner_join(df2, by = "colA") %>%
    filter(abs(colB.x - colC.y) <= 2000)

This will give you a frame with columns colA, colB.x, colC.x, colD.x, colB.y, colC.y, colD.y where the .x are from df1 and the .y are from df2. Also note that b - a <= abs(2000) is likely supposed to mean abs(b - a) <= 2000