过滤存储在列表中的数据帧的行并创建新列表

Question

我有一个包含64个数据帧的列表。 数据帧1和数据帧5必须具有相同的行名称。 与2和6,3和7相同，依此类推。 我能够运行一个for循环并创建一个新列表，但某些工作不正常：我最终得到的行数不正确。

这里一个简单的例子来重现：

# Create dataframes and store in list 
dfA <- data.frame(v1=c(1:6), v2=c("x1","x2","x3","x4","x5","x6")) 
dfB <- data.frame(v1=c(1:6), v2=c("x1","x2","x3","x4","x5","x6")) 
dfC <- data.frame(v1=c(1:5), v2=c("x1","x2","x3","x4","x5")) 
dfD <- data.frame(v1=c(1:4), v2=c("x1","x2","x3","x4")) 
example_dataframes = list(dfA, dfB, dfC, dfD) 

# These vectors give the order of the process 
vectorA = c(1,2) 
vectorB = c(3,4) 

# Create new list and start for loop 
filtered_dataframes = list() 
for (i in vectorA) { 
    for (j in vectorB) { 
df1 = example_dataframes[[i]] 
df2 = example_dataframes[[j]] 
test = intersect(df1$v2, df2$v2) 
filtered_dataframes[[i]] <- df1[which(df1$v2 %in% test),] 
filtered_dataframes[[j]] <- df2[which(df2$v2 %in% test),] 
} 
} 

在这个例子中，我希望能获得：

sapply(filtered_dataframes, nrow) 
> 5 4 5 4 

Answer 1

这个修改后的版本应该努力得到你需要的结果。

dfA <- data.frame(v1=c(1:6), v2=c("x1","x2","x3","x4","x5","x6")) 
dfB <- data.frame(v1=c(1:6), v2=c("x1","x2","x3","x4","x5","x6")) 
dfC <- data.frame(v1=c(1:5), v2=c("x1","x2","x3","x4","x5")) 
dfD <- data.frame(v1=c(1:4), v2=c("x1","x2","x3","x4")) 
example_dataframes = list(dfA, dfB, dfC, dfD) 

# Put the comparison vectors into a list. Exampl: To compare dataframes 1 and 3, put in c(1,3) 
vector.list <- list(c(1,3),c(2,4)) 

# Create new list and start for loop 
filtered_dataframes = list() 

# Loop through the list of vectors 
for (i in vector.list) { 
    # Get the first dataframe from the current vector being processed 
    df1 = example_dataframes[[i[1]]] 

    # Get the second dataframe from the current vector being processed 
    df2 = example_dataframes[[i[2]]] 

    # Get the intersection of the two dataframes 
    test = intersect(df1$v2, df2$v2) 

    # Add the first filtered dataframe to the list of filtered dataframes 
    filtered_dataframes[[i[1]]] <- df1[which(df1$v2 %in% test),] 

    # Add the second filtered dataframe to the list of filtered dataframes 
    filtered_dataframes[[i[2]]] <- df2[which(df2$v2 %in% test),] 
    }