[英]Loop through dataframe column names - R
我正在尝试遍历数据框的列名,并评估每列是哪个类。
for (i in columns(df)){
class(df$i)
}
我已经尝试了一切,除了正确的方法..
PS:我尝试这样做是因为之后我必须为每个班级设置不同的条件。
要回答确切的问题并修复给定的代码,请参见下面的示例
df <- iris # data
for (i in colnames(df)){
print(class(df[[i]]))
}
# [1] "numeric"
# [1] "numeric"
# [1] "numeric"
# [1] "numeric"
# [1] "factor"
colnames
来获取df
的列名。df[[i]]
访问每一列。 df[i]
属于data.frame
类。问题是遍历数据帧的列,并询问了一个关于遍历数据帧的某些子集的附加问题。 我使用了 mtcars 数据集,因为它的数据列比 iris 数据集多。 这允许提供更丰富的示例。 要遍历某些列子集,请在 for 循环中使用数值而不是使用列的名称。 如果感兴趣的列有规律地间隔,那么用感兴趣的列制作一个向量。 示例如下:
#Similar to previous answer only with mtcars rather than iris data.
df2<-mtcars
for (i in colnames(df2)){print(paste(i," ",class(df2[[i]])))}
#An alternative that is as simple but does not also print the variable names.
df2<-mtcars
for (i in 1:ncol(df2)){print(paste(i," ",class(df2[[i]])))}
#With variable names:
df2<-mtcars
for (i in 1:ncol(df2)){print(paste(i," ",colnames(df2[i])," ",class(df2[[i]])))}
#Now that we are looping numerically one can start in column 3 by:
df2<-mtcars
for (i in 3:ncol(df2)){print(paste(i," ",colnames(df2[i])," ",class(df2[[i]])))}
#To stop before the last column add a break statement inside an if
df2<-mtcars
for (i in 3:ncol(df2)){
if(i>7){break}
print(paste(i," ",colnames(df2[i])," ",class(df2[[i]])))}
#Finally, if you know the columns and they are irregularly spaced try this:
UseCols<-c(2,4,7,9,10)
for (i in UseCols){print(paste(i," ",colnames(df2[i])," ",class(df2[[i]])))}
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