[英]R - Aggregate data with variable name using dcast
Python
guy new to R
, so forgive the naive question. Python
家伙新R
所以原谅幼稚的问题。
I have an R
dataframe named metrics
with four columns: 我有一个名为metrics
的R
数据框,有四列:
I want to pass the level of aggregation ( day
or week
) as a variable to dcast
for aggregation. 我想将聚合级别( day
或week
)作为变量传递给dcast
进行聚合。
agg_level <- c("week")
If I hard-code week
in the in the function, it aggregates data for each week correctly: 如果我在函数中硬编码week
,它会正确地聚合每周的数据:
met <- dcast(metrics, week ~ city, value.var = count, fun.aggregate = sum)
week
NYC
CHI
SF
week
NYC
CHI
SF
2015-10-18
1
2
3
2015-10-18
1
2
3
2015-10-25
4
5
6
2015-10-25
4
5
6
If I replace week
with the variable, it fails. 如果我用变量替换week
,则失败。 (It aggregates data for all weeks.) (它汇总了所有周的数据。)
met <- dcast(metrics, agg_level ~ city, value.var = count, fun.aggregate = sum)
Output: 输出:
agg_level
NYC
CHI
SF
agg_level
NYC
CHI
SF
week
5
7
9
week
5
week
7
9
Based on this , metrics[[agg_level]]
extracts a column from variable, but this fails: 基于此 , metrics[[agg_level]]
从变量中提取列,但这会失败:
met <- dcast(m, [[agg_level]] ~ city, value.var = metric, fun.aggregate = sum)
Error in (function ... unexpected '[['
What is the correct way to do this? 这样做的正确方法是什么?
The formula argument of dcast expects that the words passed to it are column/variable names inside of the data.frame x. dcast的公式参数期望传递给它的单词是data.frame x中的列/变量名。 It does not recognize or resolve the fact that "agg_level" is a variable. 它不识别或解决“agg_level”是变量的事实。 As such, you have two options: 因此,您有两种选择:
# Option 1
# Do some text operations to make the formula based on variables.
if(this==that) {agg_level <- 'week'} else {agg_level <- 'day'}
myFormula <- sprintf("%s ~ city", agg_level)
met <- dcast(metrics, as.formula(myFormula), sum, value.var = metric)
# Option 2 - Untested
# Take advantage of dcast's alternative to the formula notation and pass a list instead.
# No idea if this will work.
met <- dcast(metrics, list(.(agg_level),.(city)), sum, value.var=metric)
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